To refrain from going on facebook for a certain period of time. This often comes after the realization that too much time has been wasted on facebook resulting in real life problems. In the even of a relapse, an individual is said to pull a triple F (see Failed Facebook Fast).
John was spending all his time on facebook instead of working. He had to go facebook fasting for a few days to catch up on his work.
the act of aimlessly exploring and in general wasting valuable time on facebook in lieu of being productive in such activities as homework, napping, etc.; usually applicable to college students
John knew that he had a sociology midterm and english paper due the next day, but ended up facebookrastinating most of the night instead.