In the UK and Ireland, adult male chickens over the age of one year are primarily known as cocks, whereas in the United States, Canada, Australia and New Zealand, they are more commonly called roosters. Males less than a year old are cockerels. Castrated roosters are called capons (surgical and chemical castration are now illegal in some parts of the world). Females over a year old are known as hens, and younger females as pullets, although in the egg-laying industry, a pullet becomes a hen when she begins to lay eggs, at 16 to 20 weeks of age. In Australia and New Zealand (also sometimes in Britain), there is a generic term chook / to describe all ages and both sexes. The young are often called chicks.
"Chicken" originally referred to young domestic fowl. The species as a whole was then called domestic fowl, or just fowl. This use of "chicken" survives in the phrase "Hen and Chickens", sometimes used as a British public house or theatre name, and to name groups of one large and many small rocks or islands in the sea (see for example Hen and Chicken Islands). The word "chicken" is sometimes erroneously construed to mean females exclusively, despite the term "hen" for females being in wide circulation, and the term “rooster” for males being that most commonly used.
In the Deep South of the United States, chickens are also referred to by the slang term yardbird.