Marauders is a semi-fannish term for the group of four friends in Harry Potter's parents' generation: James Potter, Sirius Black, Remus Lupin, and Peter Pettigrew. The name "Marauders" comes from a magical map that Harry is given in the third book -- "Marauder's Map" -- that was made by the four friends, though they are never referred to in canon as "The Marauders".
(Summary credit to fanlore.org, because I don’t want to write all that. )
(Learn more! Link: https://fanlore.org/wiki/Marauders)
