what kind of music can be called Rock Music？？

Rock Music---Musical style that arose in the U.S. in the mid-1950s and became the dominant form of popular music in the world. Though rock has used a wide variety of instruments, its basic elements are one or several vocalists, heavily amplified electric guitars (including bass, rhythm, and lead), and drums. It began as a simple style, relying on heavy, dance-oriented rhythms, uncomplicated melodies and harmonies, and lyrics sympathetic to its teenage audience's concerns — young love, the stresses of adolescence, and automobiles. Its roots lay principally in rhythm and blues (R&B) and country music. Both R&B and country existed outside the mainstream of popular music in the early 1950s, when the Cleveland disc jockey Alan Freed (1921 – 65) and others began programming R&B, which until then had been played only to black audiences. Freed's success gave currency to the term rock and roll. The highly rhythmic, sensual music of Chuck Berry, Bill Haley and the Comets, and particul