1.anything you dont know the name for
3.simile for shit, crap, turd, and other related words...
i use this word all the time so i would know - i have put alot of effort in thisdefintition
"whats thischat on the bottom of my shoe"
"ooooh, thats chat!"
"you know that chatness"
"this is the chattest thing i've ever seen mate"