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1 [[def_alternate_object_database]]alternate object database::
2 Via the alternates mechanism, a <<def_repository,repository>>
3 can inherit part of its <<def_object_database,object database>>
4 from another object database, which is called an "alternate".
5
6 [[def_bare_repository]]bare repository::
7 A bare repository is normally an appropriately
8 named <<def_directory,directory>> with a `.git` suffix that does not
9 have a locally checked-out copy of any of the files under
10 revision control. That is, all of the Git
11 administrative and control files that would normally be present in the
12 hidden `.git` sub-directory are directly present in the
13 `repository.git` directory instead,
14 and no other files are present and checked out. Usually publishers of
15 public repositories make bare repositories available.
16
17 [[def_blob_object]]blob object::
18 Untyped <<def_object,object>>, e.g. the contents of a file.
19
20 [[def_branch]]branch::
21 A "branch" is an active line of development. The most recent
22 <<def_commit,commit>> on a branch is referred to as the tip of
23 that branch. The tip of the branch is referenced by a branch
24 <<def_head,head>>, which moves forward as additional development
25 is done on the branch. A single Git
26 <<def_repository,repository>> can track an arbitrary number of
27 branches, but your <<def_working_tree,working tree>> is
28 associated with just one of them (the "current" or "checked out"
29 branch), and <<def_HEAD,HEAD>> points to that branch.
30
31 [[def_cache]]cache::
32 Obsolete for: <<def_index,index>>.
33
34 [[def_chain]]chain::
35 A list of objects, where each <<def_object,object>> in the list contains
36 a reference to its successor (for example, the successor of a
37 <<def_commit,commit>> could be one of its <<def_parent,parents>>).
38
39 [[def_changeset]]changeset::
40 BitKeeper/cvsps speak for "<<def_commit,commit>>". Since Git does not
41 store changes, but states, it really does not make sense to use the term
42 "changesets" with Git.
43
44 [[def_checkout]]checkout::
45 The action of updating all or part of the
46 <<def_working_tree,working tree>> with a <<def_tree_object,tree object>>
47 or <<def_blob_object,blob>> from the
48 <<def_object_database,object database>>, and updating the
49 <<def_index,index>> and <<def_HEAD,HEAD>> if the whole working tree has
50 been pointed at a new <<def_branch,branch>>.
51
52 [[def_cherry-picking]]cherry-picking::
53 In <<def_SCM,SCM>> jargon, "cherry pick" means to choose a subset of
54 changes out of a series of changes (typically commits) and record them
55 as a new series of changes on top of a different codebase. In Git, this is
56 performed by the "git cherry-pick" command to extract the change introduced
57 by an existing <<def_commit,commit>> and to record it based on the tip
58 of the current <<def_branch,branch>> as a new commit.
59
60 [[def_clean]]clean::
61 A <<def_working_tree,working tree>> is clean, if it
62 corresponds to the <<def_revision,revision>> referenced by the current
63 <<def_head,head>>. Also see "<<def_dirty,dirty>>".
64
65 [[def_commit]]commit::
66 As a noun: A single point in the
67 Git history; the entire history of a project is represented as a
68 set of interrelated commits. The word "commit" is often
69 used by Git in the same places other revision control systems
70 use the words "revision" or "version". Also used as a short
71 hand for <<def_commit_object,commit object>>.
72 +
73 As a verb: The action of storing a new snapshot of the project's
74 state in the Git history, by creating a new commit representing the current
75 state of the <<def_index,index>> and advancing <<def_HEAD,HEAD>>
76 to point at the new commit.
77
78 [[def_commit_object]]commit object::
79 An <<def_object,object>> which contains the information about a
80 particular <<def_revision,revision>>, such as <<def_parent,parents>>, committer,
81 author, date and the <<def_tree_object,tree object>> which corresponds
82 to the top <<def_directory,directory>> of the stored
83 revision.
84
85 [[def_commit-ish]]commit-ish (also committish)::
86 A <<def_commit_object,commit object>> or an
87 <<def_object,object>> that can be recursively dereferenced to
88 a commit object.
89 The following are all commit-ishes:
90 a commit object,
91 a <<def_tag_object,tag object>> that points to a commit
92 object,
93 a tag object that points to a tag object that points to a
94 commit object,
95 etc.
96
97 [[def_core_git]]core Git::
98 Fundamental data structures and utilities of Git. Exposes only limited
99 source code management tools.
100
101 [[def_DAG]]DAG::
102 Directed acyclic graph. The <<def_commit_object,commit objects>> form a
103 directed acyclic graph, because they have parents (directed), and the
104 graph of commit objects is acyclic (there is no <<def_chain,chain>>
105 which begins and ends with the same <<def_object,object>>).
106
107 [[def_dangling_object]]dangling object::
108 An <<def_unreachable_object,unreachable object>> which is not
109 <<def_reachable,reachable>> even from other unreachable objects; a
110 dangling object has no references to it from any
111 reference or <<def_object,object>> in the <<def_repository,repository>>.
112
113 [[def_detached_HEAD]]detached HEAD::
114 Normally the <<def_HEAD,HEAD>> stores the name of a
115 <<def_branch,branch>>, and commands that operate on the
116 history HEAD represents operate on the history leading to the
117 tip of the branch the HEAD points at. However, Git also
118 allows you to <<def_checkout,check out>> an arbitrary
119 <<def_commit,commit>> that isn't necessarily the tip of any
120 particular branch. The HEAD in such a state is called
121 "detached".
122 +
123 Note that commands that operate on the history of the current branch
124 (e.g. `git commit` to build a new history on top of it) still work
125 while the HEAD is detached. They update the HEAD to point at the tip
126 of the updated history without affecting any branch. Commands that
127 update or inquire information _about_ the current branch (e.g. `git
128 branch --set-upstream-to` that sets what remote-tracking branch the
129 current branch integrates with) obviously do not work, as there is no
130 (real) current branch to ask about in this state.
131
132 [[def_directory]]directory::
133 The list you get with "ls" :-)
134
135 [[def_dirty]]dirty::
136 A <<def_working_tree,working tree>> is said to be "dirty" if
137 it contains modifications which have not been <<def_commit,committed>> to the current
138 <<def_branch,branch>>.
139
140 [[def_evil_merge]]evil merge::
141 An evil merge is a <<def_merge,merge>> that introduces changes that
142 do not appear in any <<def_parent,parent>>.
143
144 [[def_fast_forward]]fast-forward::
145 A fast-forward is a special type of <<def_merge,merge>> where you have a
146 <<def_revision,revision>> and you are "merging" another
147 <<def_branch,branch>>'s changes that happen to be a descendant of what
148 you have. In such a case, you do not make a new <<def_merge,merge>>
149 <<def_commit,commit>> but instead just update to his
150 revision. This will happen frequently on a
151 <<def_remote_tracking_branch,remote-tracking branch>> of a remote
152 <<def_repository,repository>>.
153
154 [[def_fetch]]fetch::
155 Fetching a <<def_branch,branch>> means to get the
156 branch's <<def_head_ref,head ref>> from a remote
157 <<def_repository,repository>>, to find out which objects are
158 missing from the local <<def_object_database,object database>>,
159 and to get them, too. See also linkgit:git-fetch[1].
160
161 [[def_file_system]]file system::
162 Linus Torvalds originally designed Git to be a user space file system,
163 i.e. the infrastructure to hold files and directories. That ensured the
164 efficiency and speed of Git.
165
166 [[def_git_archive]]Git archive::
167 Synonym for <<def_repository,repository>> (for arch people).
168
169 [[def_gitfile]]gitfile::
170 A plain file `.git` at the root of a working tree that
171 points at the directory that is the real repository.
172
173 [[def_grafts]]grafts::
174 Grafts enables two otherwise different lines of development to be joined
175 together by recording fake ancestry information for commits. This way
176 you can make Git pretend the set of <<def_parent,parents>> a <<def_commit,commit>> has
177 is different from what was recorded when the commit was
178 created. Configured via the `.git/info/grafts` file.
179 +
180 Note that the grafts mechanism is outdated and can lead to problems
181 transferring objects between repositories; see linkgit:git-replace[1]
182 for a more flexible and robust system to do the same thing.
183
184 [[def_hash]]hash::
185 In Git's context, synonym for <<def_object_name,object name>>.
186
187 [[def_head]]head::
188 A <<def_ref,named reference>> to the <<def_commit,commit>> at the tip of a
189 <<def_branch,branch>>. Heads are stored in a file in
190 `$GIT_DIR/refs/heads/` directory, except when using packed refs. (See
191 linkgit:git-pack-refs[1].)
192
193 [[def_HEAD]]HEAD::
194 The current <<def_branch,branch>>. In more detail: Your <<def_working_tree,
195 working tree>> is normally derived from the state of the tree
196 referred to by HEAD. HEAD is a reference to one of the
197 <<def_head,heads>> in your repository, except when using a
198 <<def_detached_HEAD,detached HEAD>>, in which case it directly
199 references an arbitrary commit.
200
201 [[def_head_ref]]head ref::
202 A synonym for <<def_head,head>>.
203
204 [[def_hook]]hook::
205 During the normal execution of several Git commands, call-outs are made
206 to optional scripts that allow a developer to add functionality or
207 checking. Typically, the hooks allow for a command to be pre-verified
208 and potentially aborted, and allow for a post-notification after the
209 operation is done. The hook scripts are found in the
210 `$GIT_DIR/hooks/` directory, and are enabled by simply
211 removing the `.sample` suffix from the filename. In earlier versions
212 of Git you had to make them executable.
213
214 [[def_index]]index::
215 A collection of files with stat information, whose contents are stored
216 as objects. The index is a stored version of your
217 <<def_working_tree,working tree>>. Truth be told, it can also contain a second, and even
218 a third version of a working tree, which are used
219 when <<def_merge,merging>>.
220
221 [[def_index_entry]]index entry::
222 The information regarding a particular file, stored in the
223 <<def_index,index>>. An index entry can be unmerged, if a
224 <<def_merge,merge>> was started, but not yet finished (i.e. if
225 the index contains multiple versions of that file).
226
227 [[def_master]]master::
228 The default development <<def_branch,branch>>. Whenever you
229 create a Git <<def_repository,repository>>, a branch named
230 "master" is created, and becomes the active branch. In most
231 cases, this contains the local development, though that is
232 purely by convention and is not required.
233
234 [[def_merge]]merge::
235 As a verb: To bring the contents of another
236 <<def_branch,branch>> (possibly from an external
237 <<def_repository,repository>>) into the current branch. In the
238 case where the merged-in branch is from a different repository,
239 this is done by first <<def_fetch,fetching>> the remote branch
240 and then merging the result into the current branch. This
241 combination of fetch and merge operations is called a
242 <<def_pull,pull>>. Merging is performed by an automatic process
243 that identifies changes made since the branches diverged, and
244 then applies all those changes together. In cases where changes
245 conflict, manual intervention may be required to complete the
246 merge.
247 +
248 As a noun: unless it is a <<def_fast_forward,fast-forward>>, a
249 successful merge results in the creation of a new <<def_commit,commit>>
250 representing the result of the merge, and having as
251 <<def_parent,parents>> the tips of the merged <<def_branch,branches>>.
252 This commit is referred to as a "merge commit", or sometimes just a
253 "merge".
254
255 [[def_object]]object::
256 The unit of storage in Git. It is uniquely identified by the
257 <<def_SHA1,SHA-1>> of its contents. Consequently, an
258 object can not be changed.
259
260 [[def_object_database]]object database::
261 Stores a set of "objects", and an individual <<def_object,object>> is
262 identified by its <<def_object_name,object name>>. The objects usually
263 live in `$GIT_DIR/objects/`.
264
265 [[def_object_identifier]]object identifier::
266 Synonym for <<def_object_name,object name>>.
267
268 [[def_object_name]]object name::
269 The unique identifier of an <<def_object,object>>. The
270 object name is usually represented by a 40 character
271 hexadecimal string. Also colloquially called <<def_SHA1,SHA-1>>.
272
273 [[def_object_type]]object type::
274 One of the identifiers "<<def_commit_object,commit>>",
275 "<<def_tree_object,tree>>", "<<def_tag_object,tag>>" or
276 "<<def_blob_object,blob>>" describing the type of an
277 <<def_object,object>>.
278
279 [[def_octopus]]octopus::
280 To <<def_merge,merge>> more than two <<def_branch,branches>>.
281
282 [[def_origin]]origin::
283 The default upstream <<def_repository,repository>>. Most projects have
284 at least one upstream project which they track. By default
285 'origin' is used for that purpose. New upstream updates
286 will be fetched into <<def_remote_tracking_branch,remote-tracking branches>> named
287 origin/name-of-upstream-branch, which you can see using
288 `git branch -r`.
289
290 [[def_pack]]pack::
291 A set of objects which have been compressed into one file (to save space
292 or to transmit them efficiently).
293
294 [[def_pack_index]]pack index::
295 The list of identifiers, and other information, of the objects in a
296 <<def_pack,pack>>, to assist in efficiently accessing the contents of a
297 pack.
298
299 [[def_pathspec]]pathspec::
300 Pattern used to limit paths in Git commands.
301 +
302 Pathspecs are used on the command line of "git ls-files", "git
303 ls-tree", "git add", "git grep", "git diff", "git checkout",
304 and many other commands to
305 limit the scope of operations to some subset of the tree or
306 worktree. See the documentation of each command for whether
307 paths are relative to the current directory or toplevel. The
308 pathspec syntax is as follows:
309 +
310 --
311
312 * any path matches itself
313 * the pathspec up to the last slash represents a
314 directory prefix. The scope of that pathspec is
315 limited to that subtree.
316 * the rest of the pathspec is a pattern for the remainder
317 of the pathname. Paths relative to the directory
318 prefix will be matched against that pattern using fnmatch(3);
319 in particular, '*' and '?' _can_ match directory separators.
320
321 --
322 +
323 For example, Documentation/*.jpg will match all .jpg files
324 in the Documentation subtree,
325 including Documentation/chapter_1/figure_1.jpg.
326 +
327 A pathspec that begins with a colon `:` has special meaning. In the
328 short form, the leading colon `:` is followed by zero or more "magic
329 signature" letters (which optionally is terminated by another colon `:`),
330 and the remainder is the pattern to match against the path.
331 The "magic signature" consists of ASCII symbols that are neither
332 alphanumeric, glob, regex special characters nor colon.
333 The optional colon that terminates the "magic signature" can be
334 omitted if the pattern begins with a character that does not belong to
335 "magic signature" symbol set and is not a colon.
336 +
337 In the long form, the leading colon `:` is followed by an open
338 parenthesis `(`, a comma-separated list of zero or more "magic words",
339 and a close parentheses `)`, and the remainder is the pattern to match
340 against the path.
341 +
342 A pathspec with only a colon means "there is no pathspec". This form
343 should not be combined with other pathspec.
344 +
345 --
346 top;;
347 The magic word `top` (magic signature: `/`) makes the pattern
348 match from the root of the working tree, even when you are
349 running the command from inside a subdirectory.
350
351 literal;;
352 Wildcards in the pattern such as `*` or `?` are treated
353 as literal characters.
354
355 icase;;
356 Case insensitive match.
357
358 glob;;
359 Git treats the pattern as a shell glob suitable for
360 consumption by fnmatch(3) with the FNM_PATHNAME flag:
361 wildcards in the pattern will not match a / in the pathname.
362 For example, "Documentation/{asterisk}.html" matches
363 "Documentation/git.html" but not "Documentation/ppc/ppc.html"
364 or "tools/perf/Documentation/perf.html".
365 +
366 Two consecutive asterisks ("`**`") in patterns matched against
367 full pathname may have special meaning:
368
369 - A leading "`**`" followed by a slash means match in all
370 directories. For example, "`**/foo`" matches file or directory
371 "`foo`" anywhere, the same as pattern "`foo`". "`**/foo/bar`"
372 matches file or directory "`bar`" anywhere that is directly
373 under directory "`foo`".
374
375 - A trailing "`/**`" matches everything inside. For example,
376 "`abc/**`" matches all files inside directory "abc", relative
377 to the location of the `.gitignore` file, with infinite depth.
378
379 - A slash followed by two consecutive asterisks then a slash
380 matches zero or more directories. For example, "`a/**/b`"
381 matches "`a/b`", "`a/x/b`", "`a/x/y/b`" and so on.
382
383 - Other consecutive asterisks are considered invalid.
384 +
385 Glob magic is incompatible with literal magic.
386
387 attr;;
388 After `attr:` comes a space separated list of "attribute
389 requirements", all of which must be met in order for the
390 path to be considered a match; this is in addition to the
391 usual non-magic pathspec pattern matching.
392 See linkgit:gitattributes[5].
393 +
394 Each of the attribute requirements for the path takes one of
395 these forms:
396
397 - "`ATTR`" requires that the attribute `ATTR` be set.
398
399 - "`-ATTR`" requires that the attribute `ATTR` be unset.
400
401 - "`ATTR=VALUE`" requires that the attribute `ATTR` be
402 set to the string `VALUE`.
403
404 - "`!ATTR`" requires that the attribute `ATTR` be
405 unspecified.
406 +
407 Note that when matching against a tree object, attributes are still
408 obtained from working tree, not from the given tree object.
409
410 exclude;;
411 After a path matches any non-exclude pathspec, it will be run
412 through all exclude pathspecs (magic signature: `!` or its
413 synonym `^`). If it matches, the path is ignored. When there
414 is no non-exclude pathspec, the exclusion is applied to the
415 result set as if invoked without any pathspec.
416 --
417
418 [[def_parent]]parent::
419 A <<def_commit_object,commit object>> contains a (possibly empty) list
420 of the logical predecessor(s) in the line of development, i.e. its
421 parents.
422
423 [[def_pickaxe]]pickaxe::
424 The term <<def_pickaxe,pickaxe>> refers to an option to the diffcore
425 routines that help select changes that add or delete a given text
426 string. With the `--pickaxe-all` option, it can be used to view the full
427 <<def_changeset,changeset>> that introduced or removed, say, a
428 particular line of text. See linkgit:git-diff[1].
429
430 [[def_plumbing]]plumbing::
431 Cute name for <<def_core_git,core Git>>.
432
433 [[def_porcelain]]porcelain::
434 Cute name for programs and program suites depending on
435 <<def_core_git,core Git>>, presenting a high level access to
436 core Git. Porcelains expose more of a <<def_SCM,SCM>>
437 interface than the <<def_plumbing,plumbing>>.
438
439 [[def_per_worktree_ref]]per-worktree ref::
440 Refs that are per-<<def_working_tree,worktree>>, rather than
441 global. This is presently only <<def_HEAD,HEAD>> and any refs
442 that start with `refs/bisect/`, but might later include other
443 unusual refs.
444
445 [[def_pseudoref]]pseudoref::
446 Pseudorefs are a class of files under `$GIT_DIR` which behave
447 like refs for the purposes of rev-parse, but which are treated
448 specially by git. Pseudorefs both have names that are all-caps,
449 and always start with a line consisting of a
450 <<def_SHA1,SHA-1>> followed by whitespace. So, HEAD is not a
451 pseudoref, because it is sometimes a symbolic ref. They might
452 optionally contain some additional data. `MERGE_HEAD` and
453 `CHERRY_PICK_HEAD` are examples. Unlike
454 <<def_per_worktree_ref,per-worktree refs>>, these files cannot
455 be symbolic refs, and never have reflogs. They also cannot be
456 updated through the normal ref update machinery. Instead,
457 they are updated by directly writing to the files. However,
458 they can be read as if they were refs, so `git rev-parse
459 MERGE_HEAD` will work.
460
461 [[def_pull]]pull::
462 Pulling a <<def_branch,branch>> means to <<def_fetch,fetch>> it and
463 <<def_merge,merge>> it. See also linkgit:git-pull[1].
464
465 [[def_push]]push::
466 Pushing a <<def_branch,branch>> means to get the branch's
467 <<def_head_ref,head ref>> from a remote <<def_repository,repository>>,
468 find out if it is an ancestor to the branch's local
469 head ref, and in that case, putting all
470 objects, which are <<def_reachable,reachable>> from the local
471 head ref, and which are missing from the remote
472 repository, into the remote
473 <<def_object_database,object database>>, and updating the remote
474 head ref. If the remote <<def_head,head>> is not an
475 ancestor to the local head, the push fails.
476
477 [[def_reachable]]reachable::
478 All of the ancestors of a given <<def_commit,commit>> are said to be
479 "reachable" from that commit. More
480 generally, one <<def_object,object>> is reachable from
481 another if we can reach the one from the other by a <<def_chain,chain>>
482 that follows <<def_tag,tags>> to whatever they tag,
483 <<def_commit_object,commits>> to their parents or trees, and
484 <<def_tree_object,trees>> to the trees or <<def_blob_object,blobs>>
485 that they contain.
486
487 [[def_rebase]]rebase::
488 To reapply a series of changes from a <<def_branch,branch>> to a
489 different base, and reset the <<def_head,head>> of that branch
490 to the result.
491
492 [[def_ref]]ref::
493 A name that begins with `refs/` (e.g. `refs/heads/master`)
494 that points to an <<def_object_name,object name>> or another
495 ref (the latter is called a <<def_symref,symbolic ref>>).
496 For convenience, a ref can sometimes be abbreviated when used
497 as an argument to a Git command; see linkgit:gitrevisions[7]
498 for details.
499 Refs are stored in the <<def_repository,repository>>.
500 +
501 The ref namespace is hierarchical.
502 Different subhierarchies are used for different purposes (e.g. the
503 `refs/heads/` hierarchy is used to represent local branches).
504 +
505 There are a few special-purpose refs that do not begin with `refs/`.
506 The most notable example is `HEAD`.
507
508 [[def_reflog]]reflog::
509 A reflog shows the local "history" of a ref. In other words,
510 it can tell you what the 3rd last revision in _this_ repository
511 was, and what was the current state in _this_ repository,
512 yesterday 9:14pm. See linkgit:git-reflog[1] for details.
513
514 [[def_refspec]]refspec::
515 A "refspec" is used by <<def_fetch,fetch>> and
516 <<def_push,push>> to describe the mapping between remote
517 <<def_ref,ref>> and local ref.
518
519 [[def_remote]]remote repository::
520 A <<def_repository,repository>> which is used to track the same
521 project but resides somewhere else. To communicate with remotes,
522 see <<def_fetch,fetch>> or <<def_push,push>>.
523
524 [[def_remote_tracking_branch]]remote-tracking branch::
525 A <<def_ref,ref>> that is used to follow changes from another
526 <<def_repository,repository>>. It typically looks like
527 'refs/remotes/foo/bar' (indicating that it tracks a branch named
528 'bar' in a remote named 'foo'), and matches the right-hand-side of
529 a configured fetch <<def_refspec,refspec>>. A remote-tracking
530 branch should not contain direct modifications or have local
531 commits made to it.
532
533 [[def_repository]]repository::
534 A collection of <<def_ref,refs>> together with an
535 <<def_object_database,object database>> containing all objects
536 which are <<def_reachable,reachable>> from the refs, possibly
537 accompanied by meta data from one or more <<def_porcelain,porcelains>>. A
538 repository can share an object database with other repositories
539 via <<def_alternate_object_database,alternates mechanism>>.
540
541 [[def_resolve]]resolve::
542 The action of fixing up manually what a failed automatic
543 <<def_merge,merge>> left behind.
544
545 [[def_revision]]revision::
546 Synonym for <<def_commit,commit>> (the noun).
547
548 [[def_rewind]]rewind::
549 To throw away part of the development, i.e. to assign the
550 <<def_head,head>> to an earlier <<def_revision,revision>>.
551
552 [[def_SCM]]SCM::
553 Source code management (tool).
554
555 [[def_SHA1]]SHA-1::
556 "Secure Hash Algorithm 1"; a cryptographic hash function.
557 In the context of Git used as a synonym for <<def_object_name,object name>>.
558
559 [[def_shallow_clone]]shallow clone::
560 Mostly a synonym to <<def_shallow_repository,shallow repository>>
561 but the phrase makes it more explicit that it was created by
562 running `git clone --depth=...` command.
563
564 [[def_shallow_repository]]shallow repository::
565 A shallow <<def_repository,repository>> has an incomplete
566 history some of whose <<def_commit,commits>> have <<def_parent,parents>> cauterized away (in other
567 words, Git is told to pretend that these commits do not have the
568 parents, even though they are recorded in the <<def_commit_object,commit
569 object>>). This is sometimes useful when you are interested only in the
570 recent history of a project even though the real history recorded in the
571 upstream is much larger. A shallow repository
572 is created by giving the `--depth` option to linkgit:git-clone[1], and
573 its history can be later deepened with linkgit:git-fetch[1].
574
575 [[def_stash]]stash entry::
576 An <<def_object,object>> used to temporarily store the contents of a
577 <<def_dirty,dirty>> working directory and the index for future reuse.
578
579 [[def_submodule]]submodule::
580 A <<def_repository,repository>> that holds the history of a
581 separate project inside another repository (the latter of
582 which is called <<def_superproject, superproject>>).
583
584 [[def_superproject]]superproject::
585 A <<def_repository,repository>> that references repositories
586 of other projects in its working tree as <<def_submodule,submodules>>.
587 The superproject knows about the names of (but does not hold
588 copies of) commit objects of the contained submodules.
589
590 [[def_symref]]symref::
591 Symbolic reference: instead of containing the <<def_SHA1,SHA-1>>
592 id itself, it is of the format 'ref: refs/some/thing' and when
593 referenced, it recursively dereferences to this reference.
594 '<<def_HEAD,HEAD>>' is a prime example of a symref. Symbolic
595 references are manipulated with the linkgit:git-symbolic-ref[1]
596 command.
597
598 [[def_tag]]tag::
599 A <<def_ref,ref>> under `refs/tags/` namespace that points to an
600 object of an arbitrary type (typically a tag points to either a
601 <<def_tag_object,tag>> or a <<def_commit_object,commit object>>).
602 In contrast to a <<def_head,head>>, a tag is not updated by
603 the `commit` command. A Git tag has nothing to do with a Lisp
604 tag (which would be called an <<def_object_type,object type>>
605 in Git's context). A tag is most typically used to mark a particular
606 point in the commit ancestry <<def_chain,chain>>.
607
608 [[def_tag_object]]tag object::
609 An <<def_object,object>> containing a <<def_ref,ref>> pointing to
610 another object, which can contain a message just like a
611 <<def_commit_object,commit object>>. It can also contain a (PGP)
612 signature, in which case it is called a "signed tag object".
613
614 [[def_topic_branch]]topic branch::
615 A regular Git <<def_branch,branch>> that is used by a developer to
616 identify a conceptual line of development. Since branches are very easy
617 and inexpensive, it is often desirable to have several small branches
618 that each contain very well defined concepts or small incremental yet
619 related changes.
620
621 [[def_tree]]tree::
622 Either a <<def_working_tree,working tree>>, or a <<def_tree_object,tree
623 object>> together with the dependent <<def_blob_object,blob>> and tree objects
624 (i.e. a stored representation of a working tree).
625
626 [[def_tree_object]]tree object::
627 An <<def_object,object>> containing a list of file names and modes along
628 with refs to the associated blob and/or tree objects. A
629 <<def_tree,tree>> is equivalent to a <<def_directory,directory>>.
630
631 [[def_tree-ish]]tree-ish (also treeish)::
632 A <<def_tree_object,tree object>> or an <<def_object,object>>
633 that can be recursively dereferenced to a tree object.
634 Dereferencing a <<def_commit_object,commit object>> yields the
635 tree object corresponding to the <<def_revision,revision>>'s
636 top <<def_directory,directory>>.
637 The following are all tree-ishes:
638 a <<def_commit-ish,commit-ish>>,
639 a tree object,
640 a <<def_tag_object,tag object>> that points to a tree object,
641 a tag object that points to a tag object that points to a tree
642 object,
643 etc.
644
645 [[def_unmerged_index]]unmerged index::
646 An <<def_index,index>> which contains unmerged
647 <<def_index_entry,index entries>>.
648
649 [[def_unreachable_object]]unreachable object::
650 An <<def_object,object>> which is not <<def_reachable,reachable>> from a
651 <<def_branch,branch>>, <<def_tag,tag>>, or any other reference.
652
653 [[def_upstream_branch]]upstream branch::
654 The default <<def_branch,branch>> that is merged into the branch in
655 question (or the branch in question is rebased onto). It is configured
656 via branch.<name>.remote and branch.<name>.merge. If the upstream branch
657 of 'A' is 'origin/B' sometimes we say "'A' is tracking 'origin/B'".
658
659 [[def_working_tree]]working tree::
660 The tree of actual checked out files. The working tree normally
661 contains the contents of the <<def_HEAD,HEAD>> commit's tree,
662 plus any local changes that you have made but not yet committed.