What is a House System?
Harry Potter:
"sorting Hat" scene
The Sorting ceremony is a yearly ritual performed at the beginning of each school year at Hogwarts School of Witchcraft and Wizardry. It's purpose is to assign first years to one of the four school Houses: Gryffindor, Hufflepuff, Ravenclaw, or Slytherin. The Sorting ceremony is held in the Great Hall before the start of term feast, after all students have arrived at school via the Hogwarts Express. (-wikia.com)