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?" (DW: The Stolen Earth)