What is a horse's poll?

The poll is the top of the head between the ears. Because of the way a horse's skull is designed, the poll can be prone to injury (in fact, a strong enough blow to the poll can kill a horse).

The word is also sometimes used to refer to the joint between the neck and the head, for example saying a horse is "Tight through the poll" means that the animal appears to have some stiffness at the top of the neck or right where the neck and head join.