"(as) bald as a coot"의 정의 및 의미

What is the origin of the idiom "bald as a coot" and when to use it?

This idiom originates from the observation of coots, which are birds known for featherless, pale, and bald-looking patches on their heads, which gives the impression of baldness. "Bald as a coot" is used to describe someone who is completely bald. It emphasizes the person's lack of hair.