Branch states
Up-to-date
Branch is up to date with parent
Forward
Branch has at least one change whilst its parent branch is unchanged. This is the required state for merging a branch.
Behind
Parent branch has at least one change whilst the branch is unchanged. Branch can be safely rebased in this state, to bring in the parent changes.
Diverged
Branch and parent have at least one change. Branch must be rebased before it can be safely promoted, to bring in the parent changes before promoting the branch.
Stale
Branch is no longer associated with its original parent (and should be deleted).