Patrollers are users that are given access to the wiki's patrolling interface. With it, any edits that have not been looked at by anyone will be tagged with a red exclamation mark, and users that are patrollers are tasked to take a look at it and see if it is okay. If so, they can then mark it as patrolled to remove the mark. Since the mark is gone, other patrollers do not need to look at the same edit.
For a listing of patrollers, see Special:ListUsers/patroller.