In the context of a Git merge, "Fast-forward" refers to a type of merge that occurs when the branch you are merging into has not changed since the branch you are merging from was created. Instead of creating a new merge commit, Git simply moves the pointer of the branch you are merging into forward to the latest commit of the branch you are merging from.
For example, if you have a master branch and a feature branch that was created from master, and no new commits have been made to master since the feature branch was created, merging feature into master will result in a fast-forward merge. The output will indicate that the branch has been updated without creating a new commit, as Git can simply "fast-forward" the master branch to the latest commit of feature.
