Quoting from the introduction to the book accompanying the CD 'Celtic Mouth Music' (Ellipsis Arts, 1997, ISBN 1-55961-341-6):

Cheek music, chin music, lilting, diddling, gobbing, pus music, purist singing, jigging, dowdling, diddlage, reel a bouche, turlutage, kan ha diskan, port-a-beul, dandling -- for all its names both beautiful and strange, mouth music's a very basic phenomenon. Built on favourite old melodies and rhythms, on the quips that slip out of folks when they're frisky or drunk, mouth music is for making music -- especially for dancing - when there aren't instruments around. Though found in various forms throughout the world, mouth music is highly developed among the Gaels. The mesmerizing rhythms of mouth tunes made them a kind of Celtic street-corner soul music centuries ago, a tradition that has gained too little attention. Known as diddling, lilting, jigging and port-a-beul in Great Britain and Ireland, mouth music became part of the musical baggage of Scots and Irish emigrants -- driven abroad by poverty or persecution, and forced to travel light. It accompanied them to Newfoundland and Nova Scotia, where it was absorbed by Acadian and French-Canadian culture, and down into the southern Appalachians.

I'd recommend that you get a copy of this wonderful resource if you're interested in this type of music.

-- Áine