The phrase for rock from the 60s and 70s that this generations' dads listened to because they didn't now any better. The term is used by people who consider themselves cultured and varied, and refuse to believe that it's possible that people actually could like classic rock.
Dude A: *Listening to Led Zeppelin*
Dude B: Wow man, really? Dad rock?
Dude A: Shut up. I can name 10 reasons why it's better than new age music.
Dude B: *Shuts up with a sheepish look on his face*