Irving Cram was a student who began attending Hogwarts School of Witchcraft and Wizardry between 1987 and 1989. By the 1993-1994 school year, he had been made a Prefect, and was tasked with patrolling areas of the school off limits to students.
Irving is a Jewish name which means "green water".
To cram is to try to make more things fit in an enclosure then there is meant to be. This is (figuratively) what Prefects try to do all the time.
- Harry Potter and the Prisoner of Azkaban (video game) (PS2 version only)