People are familiar with Draft (email or blog) state and Send or Publish state. I would go with email analogy. So I would describe commit similar to sending an email after drafting in a thread. Here I also could undo anytime and make it a draft. Similar to forward I can clone a thread (branch out?).
Things we discussed:
- a commit is somewhat a 'save' but unlike a 'final_v1.docx'
- a commit prevents changes from being overwritten
Like taking a snapshot with a camera?
I would describe it as a stopping point, or a chunk of work that represents a finished step (however you define a step).