Meaning "Internal Chuckle". Used for instances were you
don't want to say "lol" because it sounds
dumb and you really did not laugh out loud. Rather, you gave a
little internal chuckle.
Friend: "OMG, I spilt some milk on my
floor."
You: "ic, that sucks"
Acquaintance: "Why did you only write "ic" on that video I posted on your
wall?"
You: "Because a cat who like to sit in a
sink did not make me laugh out loud. I only gave an internal chuckle."