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 a 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)