1)quite the opposite of LOL (laugh out loud)
2) works best for public places, like at libraries or on the bus, when you're laughing hysterically -- on the inside
3) when you find something quite amusing, but choose not to display your feelings too publicly
4) the way ninja laugh
Bob was about to break into hysterical laughter at Susie's text, but finding himself in a library, he simply typed back a cool "LLAN."