This list is sorted alphabetically:
Via the alternates mechanism, a repository can inherit part of its object database from another object database, which is called "alternate".
Untyped object, e.g. the contents of a file.
A non-cyclical graph of revisions, i.e. the complete history of a particular revision, which is called the branch head. The branch heads are stored in $GIT_DIR/refs/heads/.
Obsolete for: index.
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).
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.
The action of updating the working tree to a revision which was stored in the object database.
A working tree is clean, if it corresponds to the revision referenced by the current head.
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.
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.
Fundamental data structures and utilities of git. Exposes only limited source code management tools.
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).
You are waaaaay behind.
The list you get with "ls" :-)
A working tree is said to be dirty if it contains modifications which have not been committed to the current branch.
Favorite synonym to "tree-ish" by some total geeks. See http://en.wikipedia.org/wiki/Ent_(Middle-earth) for an in-depth explanation.
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.
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.
Synonym for repository (for arch people).
In git's context, synonym to object name.
The top of a branch. It contains a ref to the corresponding commit object.
A ref pointing to a head. Often, this is abbreviated to "head". Head refs are stored in $GIT_DIR/refs/heads/.
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.
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).
The default 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.
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.
The unit of storage in git. It is uniquely identified by the SHA1 of its contents. Consequently, an object can not be changed.
Stores a set of "objects", and an individual object is identified by its object name. The objects usually live in $GIT_DIR/objects/.
Synonym for 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).
To merge more than two branches. Also denotes an intelligent predator.
The default upstream branch. Most projects have one upstream project which they track, and by default origin is used for that purpose. New updates from upstream will be fetched into this branch; you should never commit to it yourself.
A set of objects which have been compressed into one file (to save space or to transmit them efficiently).
The list of identifiers, and other information, of the objects in a pack, to assist in efficiently accessing the contents of a pack.
A commit object contains a (possibly empty) list of the logical predecessor(s) in the line of development, i.e. its parents.
Cute name for core git.
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.
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.
An object is reachable from a ref/commit/tree/tag, if there is a chain leading from the latter to the former.
To clean a branch by starting from the head of the main line of development ("master"), and reapply the (possibly cherry-picked) changes from that branch.
A 40-byte hex representation of a SHA1 pointing to a particular object. These may be stored in $GIT_DIR/refs/.
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.
The action of fixing up manually what a failed automatic merge left behind.
A particular state of files and directories which was stored in the object database. It is referenced by a commit object.
To throw away part of the development, i.e. to assign the head to an earlier revision.
Source code management (tool).
Synonym for object name.
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 is called object type in git's context). A tag is most typically used to mark a particular point in the commit ancestry chain.
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".
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).
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.
A ref pointing to either a commit object, a tree object, or a tag object pointing to a tag or commit or tree object.
The set of files and directories currently being worked on, i.e. you can work in your working tree without using git at all.
Written by Johannes Schindelin <Johannes.Schindelin@gmx.de> and the git-list <git@vger.kernel.org>.
Part of the git suite