a person who sends friend requests via other peoples' friend lists and continues to request their friends and so on and so on.
You receive a friend request from someone you have never heard of from another state but you have 6 friends in common. They're likely a friend worm
This person trolls through peoples' friend lists getting added by anyone they can find to access as many friend lists as they can.
You got 2,000 friends but you don't know anybody, dude. You're just friend worming everybody, asshat.