Agree with Jed. The term Celtic does cover a broad range of music, but that's only because the people from the Celtic countries have been dispersed, mostly without a choice, to other areas of the globe. They've therefore had an influence on every English speaking country. As for performers like Enya, who started with CLANNAD (her brothers and sister), her roots are certainly Celtic and the flavor of it is still there...though she's usually lumped in that nebulous category called "New Age."