Deheubarth (lit.

"Right-hand Part", thus "the South") is a regional name for the realms of south Wales, particularly as opposed to Gwynedd (Latin: Norwallia).

It is now used as a shorthand for the various realms united under the House of Dinefwr, but that Deheubarth itself was not considered a proper kingdom on the model of Gwynedd, Powys, or Dyfed is shown by the fact it was rendered in Latin as dextralis pars or as Britonnes dexterales ("the Southern Britons") and not as a named land.

In fact, in the oldest British writers, "Deheubarth" is used for all of modern Wales to distinguish it from Y Gogledd or Hen Ogledd, the northern lands whence Cunedda and the Cymry originate.