A girl that you like, do/buy things for, yet aren't officially dating due to a variety of reasons including, but not limited to:
1. One set of parents forbids dating. 2. You want to avoid the drama that comes along with dating. 3. If one of your/her exes finds out, you/she is gunna get they butt kicked.
Guy 1: "Dude your girlfriend is Hot!"
Guy 2: "No man she's my "not girlfriend," Her Mom would kill me if she found out we're dating."
When a guy has a female friend whom he buys things for, takes out on dates, drives places, etc, yet the girl insists she is not his girlfriend (and, of course, does not put out).
If a guy takes a girl to a fancy dinner for her birthday (just the two of them), gets her a pricy gift, and is told how great a friend he is: She's his not girlfriend.