"Any song or tune from the British Isles that is not from England."

So songs in Cornish wouldn't be Celtic but things like The Dowie Dens of Yarrow would be - even though the former is from a Celtic language tradition and the latter isn't? One wonders if the original poster was meaning Celtic (as in from a Celtic language tradition) or Celtic (as in those parts of the Isles which aren't England) or Celtic (as in he means basically just Irish and Scottish type music ). I suspect it might be the latter but it is a confusing term whcih means different things to different people