A term of affection like "hugs and kisses" or "love" usually used in emails or IM conversations.
Can also be used in place of "see you later".
Taken from the noise your mouth makes when you make fish mouth movements.
Bopbop is an onomatopoeic word.
-"OK man I'll speak to you later"
-"Ciao Daniel. Bopbop x"
-"Can I give you a blow job later?"
-"Yea come round."
-"OK. Bopbop x"