Music is an art form that has been around for centuries and encompasses a wide variety of genres. A MEASURE is a unit of time in music, which is usually indicated by a bar line. HARMONY is the combination of two or more notes played simultaneously. MELODY is a succession of notes that form a recognizable tune. Strains are a series of notes that make up a MELODY. A PIECE is a composition of music, often written for a specific instrument or group of instruments. ROCK is a genre of popular music that originated in the 1950s. A SONG is a short PIECE of music with words. An AIR is a slow, lyrical MELODY. CHIN is a type of Chinese folk music. Roxy is a type of ROCK music. A SCORE is a written form of music. A SHEET is a printed form of music.