Folk

The term folk music originated in the 19th century as a term for musical folk lore. It has been defined in several ways; as music transmitted by word of mouth, music of the lower classes, music with no known composer. 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. Subgenres include folk rock, electric folk and progressive folk music.

Source : http://en.wikipedia.org/wiki/Folk_music