When a girl kneels on a couch or bed or something of the sort, and hangs her ass over the edge. You, the one who is runching, sit with your back to the bedframe or couch and your ass on the floor, and proceed to serve up some cunnilingus from below.
Lots of fun, and a little easier than when they just sit on your face. Plus, this way she can totally control the level of pressure you put on her clit and gives you lots of access to everything underneath. A little tasty treat.
"Pardon me while I go to brunch with your mom... and I don't mean at a restaurant."