A group of chickens is called a brood. You can also refer to a group of chickens as a flock, the general term used to describe a group of birds.
A group of hens (or female chickens) is called a brood, and a group of baby chicks is called a clutch.
Chickens have combs: the red floppy skin around their head and neck. These combs serve as a cooling system because chickens do not sweat like humans. They also have hollow bones, as do all birds, to make them lighter for flight. Chickens have an interesting medullary bone system that produces calcium for eggshell formation. These specialized bones are located throughout the female's body. When a chicken eats, the bird's quick digestive tract passes the food through the body in only 2.5 hours.