Here's one definition of it, Skarpi, specific to the Catholic Church: A Mass in which folk music is used as part of the service instead of liturgical music. Folk Masses came into being during the 60's and 70's.

Also, one place I found said they rely heavily on the music of Taize, but when I went to their index and looked at their list of music, I didn't see a lot of what I'd consider folk music. I may have missed something, though.

Good luck!

Ast,

kat