alternate object database

Via the alternates mechanism, a repository can inherit part of its object database from another object database, which is called "alternate".

bare repository

A bare repository is normally an appropriately named directory with a .git suffix that does not have a locally checked-out copy of any of the files under revision control. That is, all of the git administrative and control files that would normally be present in the hidden .git sub-directory are directly present in the repository.git directory instead, and no other files are present and checked out. Usually publishers of public repositories make bare repositories available.

blob object

Untyped object, e.g. the contents of a file.

branch

A non-cyclical graph of revisions, i.e. the complete history of a particular revision, which is called the branch head. The heads are stored in $GIT_DIR/refs/heads/.

cache

Obsolete for: index.

chain

A list of objects, where each object in the list contains a reference to its successor (for example, the successor of a commit could be one of its parents).

changeset

BitKeeper/cvsps speak for "commit". Since git does not store changes, but states, it really does not make sense to use the term "changesets" with git.

checkout

The action of updating the working tree to a revision which was stored in the object database.

cherry-picking

In SCM jargon, "cherry pick" means to choose a subset of changes out of a series of changes (typically commits) and record them as a new series of changes on top of different codebase. In GIT, this is performed by "git cherry-pick" command to extract the change introduced by an existing commit and to record it based on the tip of the current branch as a new commit.

clean

A working tree is clean, if it corresponds to the revision referenced by the current head. Also see "dirty".

commit

As a verb: The action of storing the current state of the index in the object database. The result is a revision. As a noun: Short hand for commit object.

commit object

An object which contains the information about a particular revision, such as parents, committer, author, date and the tree object which corresponds to the top directory of the stored revision.

core git

Fundamental data structures and utilities of git. Exposes only limited source code management tools.

DAG

Directed acyclic graph. The commit objects form a directed acyclic graph, because they have parents (directed), and the graph of commit objects is acyclic (there is no chain which begins and ends with the same object).

dangling object

An unreachable object which is not reachable even from other unreachable objects; a dangling object has no references to it from any reference or object in the repository.

dircache

You are waaaaay behind.

directory

The list you get with "ls" :-)

dirty

A working tree is said to be dirty if it contains modifications which have not been committed to the current branch.

ent

Favorite synonym to "tree-ish" by some total geeks. See http://en.wikipedia.org/wiki/Ent_(Middle-earth) for an in-depth explanation. Avoid this term, not to confuse people.

fast forward

A fast-forward is a special type of merge where you have a revision and you are "merging" another branch's changes that happen to be a descendant of what you have. In such these cases, you do not make a new merge commit but instead just update to his revision. This will happen frequently on a tracking branch of a remote repository.

fetch

Fetching a branch means to get the branch's head ref from a remote repository, to find out which objects are missing from the local object database, and to get them, too.

file system

Linus Torvalds originally designed git to be a user space file system, i.e. the infrastructure to hold files and directories. That ensured the efficiency and speed of git.

git archive

Synonym for repository (for arch people).

grafts

Grafts enables two otherwise different lines of development to be joined together by recording fake ancestry information for commits. This way you can make git pretend the set of parents a commit has is different from what was recorded when the commit was created. Configured via the .git/info/grafts file.

hash

In git’s context, synonym to object name.

head

The top of a branch. It contains a ref to the corresponding commit object.

head ref

A ref pointing to a head. Often, this is abbreviated to "head". Head refs are stored in $GIT_DIR/refs/heads/.

hook

During the normal execution of several git commands, call-outs are made to optional scripts that allow a developer to add functionality or checking. Typically, the hooks allow for a command to be pre-verified and potentially aborted, and allow for a post-notification after the operation is done. The hook scripts are found in the $GIT_DIR/hooks/ directory, and are enabled by simply making them executable.

index

A collection of files with stat information, whose contents are stored as objects. The index is a stored version of your working tree. Truth be told, it can also contain a second, and even a third version of a working tree, which are used when merging.

index entry

The information regarding a particular file, stored in the index. An index entry can be unmerged, if a merge was started, but not yet finished (i.e. if the index contains multiple versions of that file).

master

The default development branch. Whenever you create a git repository, a branch named "master" is created, and becomes the active branch. In most cases, this contains the local development, though that is purely conventional and not required.

merge

To merge branches means to try to accumulate the changes since a common ancestor and apply them to the first branch. An automatic merge uses heuristics to accomplish that. Evidently, an automatic merge can fail.

object

The unit of storage in git. It is uniquely identified by the SHA1 of its contents. Consequently, an object can not be changed.

object database

Stores a set of "objects", and an individual object is identified by its object name. The objects usually live in $GIT_DIR/objects/.

object identifier

Synonym for object name.

object name

The unique identifier of an object. The hash of the object's contents using the Secure Hash Algorithm 1 and usually represented by the 40 character hexadecimal encoding of the hash of the object (possibly followed by a white space).

object type

One of the identifiers "commit","tree","tag" or "blob" describing the type of an object.

octopus

To merge more than two branches. Also denotes an intelligent predator.

origin

The default upstream repository. Most projects have at least one upstream project which they track. By default origin is used for that purpose. New upstream updates will be fetched into remote tracking branches named origin/name-of-upstream-branch, which you can see using "git branch -r".

pack

A set of objects which have been compressed into one file (to save space or to transmit them efficiently).

pack index

The list of identifiers, and other information, of the objects in a pack, to assist in efficiently accessing the contents of a pack.

parent

A commit object contains a (possibly empty) list of the logical predecessor(s) in the line of development, i.e. its parents.

pickaxe

The term pickaxe refers to an option to the diffcore routines that help select changes that add or delete a given text string. With the --pickaxe-all option, it can be used to view the full changeset that introduced or removed, say, a particular line of text. See gitlink:git-diff[1].

plumbing

Cute name for core git.

porcelain

Cute name for programs and program suites depending on core git, presenting a high level access to core git. Porcelains expose more of a SCM interface than the plumbing.

pull

Pulling a branch means to fetch it and merge it.

push

Pushing a branch means to get the branch's head ref from a remote repository, find out if it is an ancestor to the branch's local head ref is a direct, and in that case, putting all objects, which are reachable from the local head ref, and which are missing from the remote repository, into the remote object database, and updating the remote head ref. If the remote head is not an ancestor to the local head, the push fails.

reachable

All of the ancestors of a given commit are said to be reachable from that commit. More generally, one object is reachable from another if we can reach the one from the other by a chain that follows tags to whatever they tag, commits to their parents or trees, and trees to the trees or blobs that they contain.

rebase

To reapply a series of changes from a branch to a different base, and reset the head of that branch to the result.

ref

A 40-byte hex representation of a SHA1 or a name that denotes a particular object. These may be stored in $GIT_DIR/refs/.

refspec

A refspec is used by fetch and push to describe the mapping between remote ref and local ref. They are combined with a colon in the format <src>:<dst>, preceded by an optional plus sign, +. For example: git fetch $URL refs/heads/master:refs/heads/origin means "grab the master branch head from the $URL and store it as my origin branch head". And git <<def_push,push>> $URL refs/heads/master:refs/heads/to-upstream means "publish my master branch head as to-upstream branch at $URL". See also gitlink:git-push[1]

repository

A collection of refs together with an object database containing all objects which are reachable from the refs, possibly accompanied by meta data from one or more porcelains. A repository can share an object database with other repositories.

resolve

The action of fixing up manually what a failed automatic merge left behind.

revision

A particular state of files and directories which was stored in the object database. It is referenced by a commit object.

rewind

To throw away part of the development, i.e. to assign the head to an earlier revision.

SCM

Source code management (tool).

SHA1

Synonym for object name.

shallow repository

A shallow repository has an incomplete history some of whose commits have parents cauterized away (in other words, git is told to pretend that these commits do not have the parents, even though they are recorded in the commit object). This is sometimes useful when you are interested only in the recent history of a project even though the real history recorded in the upstream is much larger. A shallow repository is created by giving the --depth option to gitlink:git-clone[1], and its history can be later deepened with gitlink:git-fetch[1].

symref

Symbolic reference: instead of containing the SHA1 id itself, it is of the format ref: refs/some/thing and when referenced, it recursively dereferences to this reference. HEAD is a prime example of a symref. Symbolic references are manipulated with the gitlink:git-symbolic-ref[1] command.

tag

A ref pointing to a tag or commit object. In contrast to a head, a tag is not changed by a commit. Tags (not tag objects) are stored in $GIT_DIR/refs/tags/. A git tag has nothing to do with a Lisp tag (which would be called an object type in git’s context). A tag is most typically used to mark a particular point in the commit ancestry chain.

tag object

An object containing a ref pointing to another object, which can contain a message just like a commit object. It can also contain a (PGP) signature, in which case it is called a "signed tag object".

topic branch

A regular git branch that is used by a developer to identify a conceptual line of development. Since branches are very easy and inexpensive, it is often desirable to have several small branches that each contain very well defined concepts or small incremental yet related changes.

tracking branch

A regular git branch that is used to follow changes from another repository. A tracking branch should not contain direct modifications or have local commits made to it. A tracking branch can usually be identified as the right-hand-side ref in a Pull: refspec.

tree

Either a working tree, or a tree object together with the dependent blob and tree objects (i.e. a stored representation of a working tree).

tree object

An object containing a list of file names and modes along with refs to the associated blob and/or tree objects. A tree is equivalent to a directory.

tree-ish

A ref pointing to either a commit object, a tree object, or a tag object pointing to a tag or commit or tree object.

unmerged index

An index which contains unmerged index entries.

unreachable object

An object which is not reachable from a branch, tag, or any other reference.

working tree

The set of files and directories currently being worked on, i.e. you can work in your working tree without using git at all.