What is the Full Form of LMAO ?

LMAO - Laughing My A** Off

Laughing My A** Off is used when someone finds something very EXTREMELY funny. It is used to indicate great amusement, usually exaggerated at something. LMAO is very versatile acronym, you can use it to mean a lot of different things. So, it should be  used very carefully because it may be mis-interpreted.

Where to use LMAO
It is an internet slang which can be used while chatting as well as in sending any e-mail or a text message, but should be used carefully.