A woman you do girlfriendy things with only on occasion, or for a knowingly shortnded period of time, usually with no intent of a further relationship, aka no strings. These girlfriendy things work for both people, as they now have a date for an event, and likely a good time after the party!
Man, did you see "Up in the Air" with George Clooney, he thought he had a rental girlfriend!
You going up to see that rental girlfriend, Ronni? Sucks you have to wear a suite though, maybe go for a romp in the sack before she heads back to SD?