Tell me some points about Foljk music using the given paragraph as a reference

Folk music is a music genre that includes traditional folk music and the contemporary genre that evolved from the former during the 20th-century folk revival. Some types of folk music may be called world music. Traditional folk music has been defined in several ways: as music transmitted orally, music with unknown composers, music that is played on traditional instruments, music about cultural or national identity, music that changes between generations (folk process), music associated with a people's folklore, or music performed by custom over a long period of time. It has been contrasted with commercial and classical styles. The term originated in the 19th century, but folk music extends beyond that.

1. During the 20th century's folk revival, traditional folk music and the contemporary genre that resulted from it both fell under the umbrella term of folk music.
2. Some folk music subgenres may be referred to as world music. Traditional folk music has been described in a variety of ways, including as music that has been passed down orally, has unknown composers, is played on traditional instruments, is about cultural or national identity, changes between generations (folk process), is connected to a people's folklore, or is performed as part of long-standing custom.
3. It has been put in opposition to classical and commercial styles.