"ROFL" is often spelled all uppercase, but can also be spelled "rofl". Both versions mean the same thing. Just be careful not to type entire sentences in uppercase, as that is considered rude shouting.
Example of ROFL usage:
- (first user:) Oh, man, my boss just came to my cubicle. I was so embarrassed for him because his fly was open, and I didn't have the courage to tell him.
- (second user:) ROFL! You mean he just talked to you with his front door open the whole time! LOL!
The ROFL expression, like many cultural curiousities of the Internet, is a part of modern English communication.
Read more Internet abbreviations and shorthand expressions...