One of the school houses in Hogwarts. Founded by Salazar Slytherin. 

The Slytherin symbol is a snake. The resident ghost is the Bloody Baron. 

Harry's arch-enemy, Draco Malfoy, Crabb and Goyl are in Slytherin. 

Professor Severus Snape is head of Slytherin house.

Well-known students: Draco Malfoy, Vincent Crabbe, Gregory Goyl, Malcolm Baddock, Bole Bletchley,  Millicent Bulstrode,  Derrick, Terrence Higgs, Montague, Pansy Parkinson, Adrian Pucey, Warrington, Blaise Zabini 

Other characters from this house: Severus Snape, Lucius Malfoy, Narcissa Malfoy, Mr. Crabb, Mr. Goyl, Tom Marvolo Riddle ( Lord VOLDEMORT !! )

 About Salazar Slytherin: 

One of the four whiches and wizards who founded Hogwarts. Slytherin house is named after him. He created the Chamber of Secrets. Salazar Slytherin insisted that only pureblood children could attend the school. The other founders were against him so he left the school. Before leaving he built a room called The Chamber Of Secrets.There he sealed an unknown horror that could only be freed by his true heir to purge the school of those unworthy to study magic.