What is rollback?
Rollback is an extension used for anti-vandalism and undoing multiple bad edits. A user that is granted with the tool can see a [rollback] link in page history, on the topmost edit. By clicking this link, all edits by that contributor are reverted into the last edit by someone else, in one click of the mouse. The edit summary for the action is "Reverted edits by Example (talk | block) to last version by Example2". This is most useful for reverting vandalism quicker.
It should be noted that all administrators have the tool by default.
To request for rollback rights click here.