Need help understanding a sexual term?

I was out one night last week and meet this girl. We flirted a lot and made out some, but nothing else. We have talked on the phone a couple times and even talked about having sex probably the next time we see each other in private. Long story short she says that when we do I should be prepared to have a little "SD" afterwards. I said "What!? and STD?" She says "hahaha, no silly, you might just have a little bit of SD...hey I gotta go, see you Thursday" OK...so what is SD????