A Buttload is an actual unit of measurement.
Please don't get us in trouble with your parents if they give you a hard time for this, but a buttload is a real unit of measurement that is used for reasons that aren't always juvenile. A butt is actually a traditional unit of volume that is used for wines and other alcoholic beverages.
A butt is defined to be 2 hogsheads, which in the US is 63 gallons. So now you know… a buttload is when you have a ton of booze and you don't want to count in hogsheads.