Lmao is an abbreviated term for "Let's meet at once ."
Often used by drug dealers & criminals as a secret code, be weary of this term as it can mean that a person is trying to meet with you and probably has bad intentions.
John: "hey Mick, how's it going, do you have have the good stuff brah?"
Mick: "yea, no worries mate, llmao."
John: "alright I'll be at the place."