SVN tags and branches correspond quite closely to Git tags and branches, I think; "tag" is a naming of a commit, "branch" is an evolving repository that shares history (and perhaps future, if merged) with other such "branches".
Except Git tracks history of the named branch in the reflog, and SVN (and others, I would guess) track it inside the repository. This is a huge difference for archeologists, but quite minor in practice from my experience.
Git doesn't really have a technical difference between a tag and a branch either. They are both files containing a hash for some commit. Tags are just more cumbersome to move (branches are moved on new commits), and they can be signed cryptologically(is that a word?).
Except Git tracks history of the named branch in the reflog, and SVN (and others, I would guess) track it inside the repository. This is a huge difference for archeologists, but quite minor in practice from my experience.