When one engages in sex chat via facebook chat. Oftentimes dirty pictures are exchanged as one describes the details of the fantasy sexual encounter. If one so chooses, participants may masturbate while doing the one handed typing/clicking move typical of online porn perusing.
"Dude, I totally booked up with my ex last night. It was hot." "I didn't know that booking up was cheating!" "My mom totally walked in on me when I was booking up with Susie."