Flavorwire has a post on the etymology of 10 musical genre names. This is the type of thing that you wonder about from time to time, but probably never bothered to look up.
Punk: While “punk” was once (and still, occasionally) catch-all slang for a young delinquent, “punk rock” first appeared in a 1970 Chicago Tribune article, uttered by Ed Sanders of The Fugs. Although the band was one of punk’s immediate ancestors, Sanders went on to define the term as “redneck sentimentality.” The next year, Dave Marsh of Creem used “punk rock” to describe ? and the Mysterians. Its meaning evolved from there, originally encompassing a slew of Nuggets-era garage-rock bands and eventually solidifying into a more rigid description of the mid-’70s bands we think of as “punk.”