noun. Short for "nuckle tattoos," or small tattoos that appear across the knuckles. Usually a series of small tattoos near a person's nuckles that when put together (ie. a fist is made and two hands are placed next to each other) form a complete message. Typically one letter on each finger and not the thumbs.
That nerd tried to be all cool with his lame "DONTPANC" knucktat. He should have gone for something better, like "SAND" on right hand and "WICH" on left hand. You know, as in a knuckle sandwich.