An internet acronym which stands for "That made me laugh." It is used when "Ha ha" or "Lol" simply aren't enough, and also when you are too lazy to write out the full four-word sentence.
Created by the legendary Funky_Del as a more fitting replacement for lol; means "That made me lick my balls!". To be more precise, lol in messaging services nowadays is more of a general part of a sentence, like a full stop or comma, than to mean you actually "laughed out loud", and in contrast "lmao" seems too much to use for things that are only vaguely funny. Therefore, tmmlmb was created.