1) A friend that you have no feelings for but happen to hookup with. This is usally an agreed upon relationship that is hidden from your other friends. Mostly driven by alcohol but also sober- who deosn't want sober and drunk action?
2) The aftermath of a broken relationship. An ex-couple still wants to have someone to hookup with. No strings attached. Just fun.
Texts after a casual hookup the night before.
Girl: Sorry about last night.
Guy: Don't be. It was fun.
Girl: hahah yeah i guess it was.
Guy: Well then, now that that is settled. Want to come to my room tonight?
Girl: uh.. what would this entail?
Guy: Relax. No strings attached. We can be hookup friends.