blackhead

Short definition from Wiktionary

Noun

1. 1
   A type of comedo, a skin blemish, a type of acne vulgaris, where a pore becomes clogged with a dark, hard, cheesy keratin-filled substance forming a hard black "head" on the skin's surface.
2. 2
   A form of histomoniasis in poultry, characterized by cyanotic discoloration on the bird's head.
3. 3
   A scaup: any of various ducks of the genus Aythya.