What is Slytherin house in Harry Potter?

Salazar Slytherin was one of the four founders of Hogwarts School of Witchcraft and Wizardry.

Voldemort (Tom Marvelo Riddle) was a direct descendent of Slytherin.

The other founders are Rowena Ravenclaw, Godric Gryffindor and Helga Hufflepuff.