dork disc
Also known as a "spoke protector", which is commonly found on inexpensive department store bicycles along with with kickstands, front baskets, and handlebar tassels. It's unnecessary if you're bike is properly maintained. The sundamaged dork disc is a telltale sign of a newbie rider.
Dude, you don't need that dork disc if your derailleurs are properly indexed. If you're not using training wheels, chuck it in the trash.