When you publish a version, we usually first hit in a repository label (tag), so that it uniquely identifies the moment of playing tag version. Whenever the future, take a label version, is the version of history that will tag the time taken out. Therefore, the label is a snapshot of the repository.
Although the label is a snapshot of the Git repository, but in fact it is a pointer to a commit (with branches like right? But the branches can be moved, the label can not move), so, create and delete tags are instantaneous.
Git has commit, why the introduction of tag?
"Please put that version on Monday packaged and released, commit number is 6a5819e ..."
"Digital's hard to find a bunch of mess!"
If you change one way:
"Please put that version on Monday packaged and released, the version number is v1.2"
"Well, look commit accordance tag v1.2 on the line!"
So, tag people is a meaningful name easy to remember, it is tied together with a commit.