Fast-forward

what is git rebase Source: atlassian: Pull Request Merge Strategies

A fast-forward merge can only happen if in master there are no more recent commits than the commits of the feature branch. In this case master's HEAD can easily be moved to the latest commit of the feature branch. And the merge can complete without an explicit merge commit: it literally just fast-forwards the branch label to the new commit.

Differently than rebase, a fast-forward merge will not change the commit ids (sha-1), but it will still lose the context of those commits as part of an earlier feature branch.