An e-mail term much like LOL. It stands for Laughing In My Head Silently.
Commonly used when a joke is not LOL-worthy, and not too funny. Just mildly funny.
"Ohmigod, did you hear that joke about the rabbi and the frog? Total LIMHS."
Laughing in my head silently
used when you think something's funny but you're not actually laughing out loud.
LIMHS, that was pretty funny.