The kind of music you listen to only because your girlfriend (or any girl(s) you like) does. When your macho friends flip through your record collection and quizzically ask why you have this winsome indie-pop record mixed in with your slovenly punk or your metal or whatever else you bro down to with your dude friends, "girlfriend rock" is the excuse you give. If they continue to make fun of you, ask them why they never get any? Or do they really enjoy jugga-lette hookups that much?
Dude 1: "What are these doing in your glove box...Blank Dogs? Belle and Sebastian???"
Dude 2: "Oh, that's what my girlfriend likes to listen to."
Dude 1: "You don't actually like this shit, do you?"
Dude 2: "Actually...for girlfriend rock, you can do a lot worse. Have you heard Real Estate?"