A "Couch Girl" is a female who will go back to a male's apartment, particularly for intercourse, even if the guy is crashing on the couch and doesn't actually own a bed.
Lisa is a Couch Girl...she totally went home with Steve last night and he's in between apartments!
A girl that is in rotation on the couch. One who sits on the couch staring blankly at the tv (be it a movie or a single player game) while the guy next to her randomly leaves her to go hit on other girls on AIM. Couch girls, not getting the hint, will proceed to insist upon staying the night and making the guy as uncomfortable as possible.
"I can hear the couch girl squeal at the scary parts, but I bet she's not really scared."
Sometimes couch girls get promoted to bed girls
"Now all she does is sit on his bed watching him play WoW. At least she got promoted from couch girl."