Stands for "Laugh Out Loud, Oh Shit I Really Laughed Out Loud"
The term was coined by Christopher DiSarcina and can be used in a conversation on the internet for when something is funny and you actually laugh out loud. It is more or less the equivalent to LMFAO!!!
You: Hey man I just found this funny ass picture!
*you show your friend*
Your Friend: LOLOSIRLOL! Oh man that is fucking epic!