A specialization of music. A very broad category of popular music that began in the mid-1950s and continues up to the present day (1999), and that encompasses a variety of submovements and styles. Essentially a youth-oriented music. rock music is usually played on electrically-amplified instruments (esp. the electric guitar), often in a loud and aggressive manner. The lyrics ofrock music songs (in addition to the common popular music themes of romantic love, sexual desire, and loneliness) often express rebellion and independence.