Hi gillymor

A source singer is one who learned traditional songs in their original context. Such as Walter Pardon, Fred Jorden or the Copper family. I think the term came about because they were the source for a lot of the collections that revival artists now use. I'm sure someone will correct me if I'm wrong :-)

Social is ceilidh or barn dancing - Socialy! Ritual is such dances as Morris, Rapper, Molly etc.

Hope this helps.