Cambria is a name for Wales, being the Latinised form of the Welsh name for the country, Cymru. The term was not in use during the Roman (when Wales had not come into existence as a distinct entity) or the early medieval period. After the Anglo-Saxon settlement of much of Britain, a territorial distinction developed between the new Anglo-Saxon kingdoms (which would become England and Southern Scotland) and the remaining Celtic British kingdoms (which would become Wales and, before their absorption into England, Cornwall to the south and Strathclyde or Hen Ogledd to the north). Latin being the primary language of scholarship in Western Christendom, medieval writers commonly used either the older term Britannia, as the territory still inhabited by Britons, or Wallia, a term derived from Old English, to refer to Wales. The term Cambria is first attested in Geoffrey of Monmouth in the 12th century as an alternative to both of these, since Britannia was now ambiguous and Wallia a foreign import, but remained rare until late in the Middle Ages.

Source: https://en.wikipedia.org/