What is the concept behind labels

I new to GIT and gitlab and just set up my first instance and I’m starting to use. Trying to understand what LABELs are. I am use to labels be used to tag or identify code at a known point in time, But the concept seems different here. I read a couple of posts but I do not see anything that gives me a go overview of what they are, why I use them and how I apply them.

Can somebody help and point me to some good documentation?

Thanks, E