Clom (alternatively spelt Klom) is the twin planet of Raxacoricofallapatorius. The inhabitants of both worlds are similar in physical characteristics, but seem to despise each other nonetheless.
The Abzorbaloff is a native of Clom. (DW: Love & Monsters)
Clom is also sworn on by a Slitheen as "for the love of Clom". (SJA: Revenge of the Slitheen)
Clom was one of the 27 planets "stolen" into the Medusa Cascade, to which the Doctor replied "Who'd want Clom?" Clom was later returned by The Doctor, the Clone Doctor and Donna Noble to its correct place. (DW: The Stolen Earth/DW: Journey's End)