Meaning of Github Ahead/Behind Metrics

Question

In plain language (hopefully with a simple example), what do the ahead/behind metrics on a Github repo\'s branch mean?

And what are the implications for that branch

Answer 1

If you're more of a visual type, take a look here:

◈ - ◈ - A - ◈ - B
      \
        ◈ - C

A is 2 commits behind and 0 commits ahead of B
B is 0 commits behind and 2 commits ahead of A
C is 1 commit behind and 2 commits ahead of A
C is 3 commits behind and 2 commits ahead of B

So "behind" means the other branch has commits this one doesn't, and "ahead" means this branch has commits the other does not.