To "friend" someone on Facebook whom you haven't seen or talked to in years just to see what they look like, if they've gotten fat, have ugly kids, or otherwise see how their life sucks compared to yours. Also, you have no intention of ever writing on this person's wall or commenting on a status or picture, because you are just there to see what they look like/are doing now. Could also go the other way - they could totally rock and make you feel bad, in which case you will un-friend them.
You: Hey, I got an email from Kimmy from High School the other day.
Me: Really? You guys weren't even friends though, right?
You: Hmmm, I guess not.
Me: Dude, she is totally facestalking you.