2 people, mainly a dude and a chix, pressed tight against one another in a way that their hotspots (genitals) are makin' contact. This usually happens during intimate kissing and hugging. It can be standing up or sitting or laying down but is usually with clothes still on. Not dryhumping, just as it says, "Pressed up"
dude: damn we got all pressed up 2day, that wuz hawt
chix: god i wanted to grind u today