What is the Full Form of ROFL ?

ROFL - Rolling On Floor Laughing

Rolling On Floor Laughing (ROFL) is an internet slang which can be used while chatting as well as in sending any e-mail or a text message. Originally it was used only in text-based communication but now it is often spoken, and is pronounced roffle.

Let's see an example of a little conversation between two unknown person, using ROFL :-
Person1 : Hi!
Person2 : hi
Person1 : I just sliped from the stairs
Person2 : ROFL

He is not literally rolling on the floor laughing, it is an exaggeration of something extremely funny. Its kind of like lol (laugh out loud) except its used when something REALLY funny happens.