Defining Rock Music
Rock music has its roots in 1940s and 1950s rock and roll and rockabilly, which evolved from blues, country music and other influences. In the late 1960s, rock music was blended with folk music to create folk rock, blues to create blues-rock and with jazz, to create jazz-rock fusion, and without a time signature to create psychedelic rock. Also in the 1970s, rock developed a number of sub-genres, such as soft rock, heavy metal, hard rock, progressive rock, and punk rock. Rock sub-genres that emerged in the 1980s included synth-rock, hardcore punk and alternative rock.
Source:
Wikipedia