The definition of "hooking up".
Back when I first started college, hooking up with someone meant to make out with that person. Then a few years later, it started to mean having sexual relations with someone. So what happened? Did the general population just get sluttier and we had to adjust definitions to fit?
This is a great definition that helps explain it, from http://www.urbandictionary.com :
to engage in any type of sexual activity.
1. purposely ambiguous, equivocal word to describe almost any sexual action. usually used to exaggerate or minimize what exactly happened. a hook-up can range from a make-out session to full out sex.
2. person you hook up with
a: "so what did you guys do last night."
b: "welll, you know...we hooked up."
a: "come on! that could mean anything. give me details!