HOw do you define rock music?

THE TEXT BOOK DEFINITION........... Rock is a form of popular music from the mid 20th century which typically features a vocal melody (often with vocal harmony) that is supported by accompaniment of electric guitars, a bass guitar, and drums, often with a strong back beat. Keyboard instruments such as organ, piano, or synthesizers are often used in many types of rock music. While brass and woodwind instruments, such as saxophone were common in some styles in earlier development of rock, they are less common in the newer subgenres of rock music since the 1990s. The genre of rock music is broad, and its boundaries loosely-defined, with related genres such as soul and funk sometimes being included in the definition of the term.