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