A body piercing consisting of an adornment attached to the lip.
2007, Margo DeMello, “Labrets”, entry in Encyclopedia of Body Adornment, page 175,
A labret is a piercing that is attached below the lower lip, above the chin.
Also known as the “Mao” (because it looks like the mole above Mao Zedong's chin), the jewelry used in the labret is usually a labret stud, which of a metal shaft with a simple round stud protruding from the face; it is attached inside of the lip with a flat piece of backing metal.