"FaceBook friend" maps roughly to "Anyone I have had some form of contact with and either don't actively hate, who says things I'm interested in hearing, or who I haven't gotten around to deleting". It's a completely distinct concept from "friend", in my mind. A FaceBook friend could be more accurately be described as a "contact", the way that I usually see it used.
I know some people who are deep in the FB Kool-Aid, or who label all acquaintances as "friends", but that doesn't accurately describe most of the people around me.
See someone from your hallway in your dorm in the library you never spoke to before? Oh dude that's my boy from my dorm right there!
See a classmate out at the bar that you only asked for homework a few times? "Sup dude! It's your boy from chem class!"
And hundreds of other examples similar to this.