> I've somehow created a branch that couldn't be deleted.

The problem here is one of conflicting terminology. What Git calls a branch, no other version control system calls a branch. A branch in Git is really a moving pointer to the head of a branch as other VCSs would see it.

The confusion can go both ways, by the way. I.e. when a user who is used to another VCS expects a branch to be a persistent label for a set of commits and then discovers that it doesn't work like that for Git repositories and that your branches may "move" or "disappear" and don't even describe sets of commits but individual commits.

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.

In SVN there really is no technical difference between a tag and a branch IIRC, although their intended usages are different, as you say.

To the point where it's almost easiest to say SVN doesn't have branches or tags - it just has directories and conventions.

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?).