What’s the difference between tag and branch in git?

When writing the backend logic with jgit, I realize that git checkout will be executed with a priority, i.e, first checkout the branch and then the tag.

A tag represents a version of particular moment in a branch. A branch represents a separate thread of development where you can push the evolutions and it may be merged into the main workflow. Usually, a tag allows to recreate a version from it, e.g, a released version. While a branch contains the on-going updates on a particular version. You’ll make a main line branch based on a particular version and separate a particular branch for fixing a bug or for delivering to a client. And eventually, these branches will be merged back to the main line.

More technical:

• tags reside in refs/tags/ namespace, and can point to tag objects (annotated and optionally GPG signed tags) or directly to commit object (less used lightweight tag for local names), or in very rare cases even to tree object or blob object (e.g. GPG signature).
• branches reside in refs/heads/ namespace, and can point only to commit objects. The HEAD pointer must refer to a branch (symbolic reference) or directly to a commit (detached HEAD or unnamed branch).
• remote-tracking branches reside in refs/remotes/<remote>/ namespace, and follow ordinary branches in remote repository <remote>

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