Chickens (Gallus gallus domesticus) are a domesticated species of bird and a subspecies of the red jungle fowl (Gallus gallus) of Asia. Chickens are one of the most well known and widespread of all domesticated animals, and can be found on every continent except Antarctica. Humans keep chickens for a variety of reasons, including for pets, eggs, and meat, as well as showing and breeding. Chickens have even become a popular backyard pet for people living in cities and towns. They are so well known that they are often portrayed in media, often very inaccurately.
Hens are sometimes referred to simply as 'chickens' with roosters being separate (e.g. 'Four chickens and one rooster for sale), when in fact they are both chickens and should both be referred to as such. Sometimes the opposite is true, where roosters will be referred to as 'chickens' and hens simply as 'hens'. All individuals of the species Gallus gallus domesticus can be referred to as chickens, no matter the age, breed, or sex.