Sage Of The Wise wrote:I think it meens "Rolling on floor laughing".
The precise meaning is "Roll on the floor laughing." It's phrased as an imperative, just like "LOL" is for "laugh out loud." (I don't know why they're imperatives, however.)
It was originally "ROTFL," but the "T" has been largely dropped since it went into common Internet usage.
Lest you question how I could assign a precise phraseology to this common sequence of letters, let me assure you that there are purists at MIT who keep track of what these and many other MIT-originated expressions originally (they would say, properly) meant.
(For another example, consider the term "flame." This is a backformation from "flamer," MIT slang for "flaming asshole." In its original MIT manifestation, to flame meant "to speak obnoxiously and/or at great length," and it is from this that the current usage of "flame" is derived.)