Recently I saw a picture on Facebook which was funny. Actually, it wasn't funny as much as witty. Either way, I commented on it and wrote "lol =)". Clearly I was not actually laughing, nor was the picture funny in the actual sense of the word. So why LOL?
Understanding the real meaning behind LOL requires understanding of the real meaning behind laughter.
Laughter is an expression of positiveness and approval. More powerful than any word, laughing at something or someone is a strong opinion of an underlying aspect of the situation. It doesn't have to be funny; it can be ridiculous, witty, subtle or even cruel and mocking. In essence, the word LOL has replaced actual laughter in situations where actual laughter simply isn't provoked. Yes, some pictures on Facebook are funny, but they're not REALLY that funny, and some jokes are witty but don't make us laugh.
Sometimes, LOL is used to approve of disapproving something.
"She bought a real fur coat, then binned it because the fashion changed"
This explains the sometimes ridiculous situation where a group of friends or acquaintances laugh together, despite some or most of them not really finding anything funny. They do it out of willingness to be part of the same frame of mind or group, maybe to facilitate getting closer to someone they fancy.