When an individual (male or female) scours another individual's profile, frequently checks their status updates, or reads their wall posts to and from other people. This is usually done either because the individual wants to know as much as possible about the individual whose profile they are reading, or they're bored and haven't looked at that person's profile yet after they've gained them as a friend on facebook. Some people admit to it, other's deny they have been doing it, even when caught in the act.
Joe: "Dude what are you doing?"
Mike: *Looks up from ex-girlfriend's profile, whom he is facebook stalking* "Nothing."
Joe: *Sees ex-girlfriend's profile page* "Quit facebook stalking that chick and come play Xbox"
Mike: "I wasn't facebook stalking her!"