The act of sliding one's penis between the ass cheeks of another; sliding the "hot dog" between the "buns".
"Wendy giggled as she gave her male friend Mike an assjob". Many people in today's society do not classify assjobs as sexual activity; they are more like massages, and thus can be shared between friends.
When a girl lubes up a guys cock and gently grinds her ass cheeks on and gets him off. That or he lays his cock between her ass cheeks and strokes away without penetration.
Stacy has such a soft sexy ass. I love it when she lets me lube it up and lay my cock between those cheeks and grind on it for a great ass job.