I have seen the gaming.SE Badge "Cleanup: First Rollback" and searched for it but couldn't find anything on to what it refers.
What does this mean? How do I roll back (presumably a question, an answer or a comment)?
Rolling back a question or an answer is an option while editing it. Basically you restore (roll back to) a previous version of a post. You do this when, for example, someone abused the edit function on a question, or made an edit to your post you don't agree with.
It means that if I edit your post and you disagree with my edit, there is an option to rollback the edit.
This only applies to questions and answers