The story
Shortening of rock and roll music, in use since circa 1966 to refer to genres of popular music which had grown sufficiently distinct from 1950s rock and roll.
Etymology from Wiktionary, CC BY-SA 4.0.
rock music
Today it means: A broad genre of popular music, including especially those styles ultimately derived from rock and roll, employing electrical amplification, heavy use of guitars, 4/4 time with strong percussive rhythm on beats two and four (backbeat), and usually themes of bold wildness, rebellion, and sexuality. Full definition →