Flirting with some one over facebook chat. Like sexting
only a far less personal version where knowing the person isn't even necessary. Could be done frequently with one or multiple partners. Very common among males who met the girl the night before and didn't pull a number and instead resort to this virtual form of "spitting game."
"I've been facefucking this girl for like two weeks, we're finally going to the same party tonight hopefully I'll get lucky"
"Amber has been facefucking me all semester and still has no idea I'm not down.