The term "Celtic nations" derives from the linguistics studies of the 16th century scholar George Buchanan and the polymath Edward Lhuyd.As Assistant Keeper and then Keeper of the Ashmolean Museum, Oxford (1691–1709), Lhuyd travelled extensively in Great Britain, Ireland and Brittany in the late 17th and early 18th centuries. Noting the similarity between the languages of Brittany, Cornwall and Wales, which he called "P-Celtic" or Brythonic, the languages of Ireland, the Isle of Mann and Scotland, which he called "Q-Celtic" or Goidelic, and between the two groups, Lhuyd published Archaeologia Britannica: an Account of the Languages, Histories and Customs of Great Britain, from Travels through Wales, Cornwall, Bas-Bretagne, Ireland and Scotland in 1707. His Archaeologia Britannica concluded that all six languages derived from the same root. Lhuyd theorised that the root language descended from the languages spoken by the Iron Age tribes of Gaul, whom Greek and Roman writers called Celtic.Having defined the languages of those areas as Celtic, the people living in them and speaking those languages became known as Celtic too. There is some dispute as to whether Lhuyd's theory is correct. Nevertheless, the term "Celtic" to describe the languages and peoples of Brittany, Cornwall and Wales, Ireland, the Isle of Mann and Scotland was accepted from the 18th century and is widely used today.
These areas of Europe are sometimes referred to as the "Celt belt" or "Celtic fringe" because of their location generally on the western edges of the continent, and of the states they inhabit (e.g. Brittany is in the northwest of France, Cornwall is in the south west of Great Britain, Wales in western Great Britain and the Gaelic-speaking parts of Ireland and Scotland are in the west of those countries).Additionally, this region is known as the "Celtic Crescent" because of the near crescent shaped position of the nations in Europe.
The Continental Celtic languages were extinct by the Early Middle Ages, and the continental "Celtic cultural traits", such as an oral tradition contained in the language and that was transmitted through it, mainly disappeared, at the same time the catholic religion fought against the remains of a Celtic paganism.
Since they no longer have a living Celtic language, they are not included as 'Celtic nations'. Nonetheless, some of these countries have movements claiming a "Celtic identity"
Each of the six nations has its own living Celtic language. In Wales, Scotland, Brittany, and Ireland, these have been spoken continuously through time, while Cornwall and the Isle of Man have languages that were spoken into modern times but later died as spoken community languages. In both of the latter regions, however, revitalization movements have led to the adoption of these languages by adults and produced a number of native speakers.
Ireland, Wales, Brittany and Scotland contain areas where a Celtic language is used on a daily basis – in Ireland the area is called the Gaeltacht, Y Fro Gymraeg in Wales, and in Brittany Breizh-Izel. Generally these communities are in the west of their countries and in upland or island areas. The term Gàidhealtachd historically distinguished the Gaelic-speaking areas of Scotland (the Highlands) from the Lowland Scots-speaking areas. More recently, this term has also been adopted as the Gaelic name of the Highland council area, which includes non-Gaelic speaking areas. Hence, more specific terms such as sgìre Ghàidhlig ("Gaelic-speaking area") are now used.
In Wales, the Welsh language is a core curriculum (compulsory) subject, which all pupils study. Additionally, 20% of school children in Wales go to Welsh medium schools, where "they are taught entirely in the Welsh language". In the Republic of Ireland, 7.4% of primary school education is through Irish medium education