Last time, we looked at the origins of the phrase “to rock”–as in “That really rocks.” In the beginning–a hundred years ago–that expression was used by black jazz and R&B performers. Then it was used to describe the new music of mostly white singers in the 1950s. But in the 1970s, the pendulum swung back the other way.
The phrase “to rock” and all its conjugated forms started being used by rap and hop-hop performers. Guys like Grandmaster Flash started talking about “rockin’ the mic.” The earliest know usage of that seems to be one of his 1978 bootlegs, which to this definition of “to rock” to be included in the Oxford English Dictionary.
After hip-hop performers and fans started to rock the mic, they started to rock other things, like clothes. But in both cases, “to rock” something means to do it with style and power.