Historically, the Britons (sometimes Brythons) were the indigenous peoples inhabiting the island of Britain who can be described as Celts, before their language and culture was largely replaced by invading Anglo-Saxons. They were speakers of the Brythonic languages and shared a common culture . In terms of language and culture, the entire British Isles was mainly Celtic during this period, although only the island of Britain and Brittany was inhabited by Brythonic Celts. The inhabitants of Ireland, the Isle of Man and Dál Riata were Gaels or Gaelic Celts who spoke Goidelic languages.

It is not known whether the Picts of northern Britain were a Brythonic-speaking people. A number of scholars argue that the unknown Pictish language was Brythonic, but in Sub-Roman Britain the Picts were distinguished as a separate group, as were the Gaels of Dál Riata. Therefore, the term "Briton" or "Brython" traditionally refers to the inhabitants of ancient Britain excluding the Picts, because many Pictish cultural traits (for example their sculpture, pottery and monuments) differ from those of the Britons.

The Britons are also referred to as the ancient, native, indigenous and ethnic Britons, or alternatively the British or Brythonic tribes.