Having sex in a place or situation where the risk of getting caught adds to the thrill, the riskier and filthier the better including not using protection. Can be opportunistic or arranging a situation (setting the stage) where having sex under the nose of one or more partners increases the danger and getting away with it is the goal.
I have a fuck buddy who arranged for me to come to her boyfriend's party where no one knew we knew each other when everyone was wasted. She waited for me in a room away from the main party which could be locked and we had a danger fuck, the boyfriend even tried the door looking for her! We carried on acting like we didn't know each other afterwards and when we realised we'd gotten away with it we were so turned on we went upstairs and did it again with the door unlocked. That was a mega-danger fuck!