Deheubarth was a regional name for the realms of south Wales, particularly as opposed to Gwynedd. 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 its rendering in Latin as dextralis pars or as Britonnes dexterales and not as a named land. In the oldest British writers, Deheubarth was used for all of modern Wales to distinguish it from Hen Ogledd, the northern lands whence Cunedda originated.

Wales in the early Middle Ages covers the time between the Roman departure from Wales c. 383 until the middle of the 11th century. In that time there was a gradual consolidation of power into increasingly hierarchical kingdoms. The end of the early Middle Ages was the time that the Welsh language transitioned from the Primitive Welsh spoken throughout the era into Old Welsh, and the time when the modern England–Wales border would take its near-final form, a line broadly followed by Offa's Dyke, a late eighth-century earthwork. Successful unification into something recognisable as a Welsh state would come in the next era under the descendants of Merfyn Frych.