Definition of rocker noun from the Oxford Advanced Learner's Dictionary

rocker

noun

ˈrɒkə(r)

ˈrɑːkər

1 one of the two curved pieces of wood on the bottom of a rocking chair2 (especially North American English) = rocking chair3 Rocker (British English) a member of a group of young people in Britain, especially in the 1960s, who liked to wear leather jackets, ride motorcycles and listen to rock and roll music compare mod4 a person who performs, dances to or enjoys rock musica concert by ageing rocker, Rod Stewart

Idioms

be off your rocker

(informal) to be crazy