When a girl curls up into an egg shape then planting her face onto ground while a male with penis or female with strap on then either screws the girl in the vegina (thanks to the angle) or analy, like doggie style.
"The Egg Position"
Kelly: "Hey Jess, wanna start Egging?"
Jess: "Sure thing Kelly! kitchen or the living room?"
Kelly: "Either rooms good" (wink)
Kelly: "We can always do the next room tomorrow"
Jess: "Who's cleaning up the mess though?"
Kelly: "Ummmm........Tash will, since, after all, shes our slave"