Folk music is a term for musical folklore which originated in the 19th century. It has been defined in several ways: as music transmitted by word of mouth, as music of the lower classes, and as music with unknown composers. It has been contrasted with commercial and classical styles. Since the middle of the 20th century, the term has also been used to describe a kind of popular music that is based on traditional music. Fusion genres include folk rock, electric folk, folk metal, and progressive folk music.

source: wikipedia