Rock for short)
A genre of music (60's to current) who's heyday occurred in the 1970's. Known for blending various genres (most commonly jazz and classical) into Rock music, the genre "progresses" music to try to evolve it into something more engaging than simply something to dance or sing-a-long or jam to.
While arguable, the first Prog band is technically believed by Prog fans to be the Beatles. However, the first band to play in the current sense of the word was King Crimson.
Although most bands in the genre came from the UK, many came from the US (Frank Zappa / Dream Theatre), Canada (Rush), Germany (Van Der Graaf Generator), and more (Iceland - Sigur Ros).
Prog Rock and Metal are both considered to be "guy" bands, and contrary to popular belief, they are not meant to be listened to alone, rather it's just hard to find another prog fan near you these days.
Only 20 minutes long? Woah, that's one short Progressive Rock song...