Labret - From Wikipedia, the free encyclopedia

A labret is one form of body piercing. Taken literally, it is any type of adornment that is attached to the facial lip (labrum). However, the term usually refers to a piercing that is below the bottom lip, above the chin.

Among the ancient Aztecs and Mayans labret piercing was reserved for male members of the higher castes.

A less common name for the labret piercing is the "Mao." It is widely believed that this name originates from Mao Zedong's mole below his lower lip.

I had to check - I didn't know either!