It is a piece of fabric about 13x13 hanging from the waist covering the butt (the front/sides)sometimes with d-rings, usually plaid or pinstripe, mostly worn by the punk community.
mother: no. Now, doff me a hat, and, if you don't' like the rules in this house, you can, for a change, try and flap your own wings with your girlfriend. That'll teach you to be more independent.