Lmao basically means laugh my ass out
Trash kid: I died in fortnite
Me: lmao
lowercase lmao is always used ironically
where the person sending this makes sure to let you know that they are in fact, not laughing
friend 1: insert mediocre joke or anecdote
friend 2: .........
friend 2 : lmao
Lmao usually means "laugh my ass of" but u can also use it as Lick Me All Over