The term “chicken” encompasses all domesticated birds of the species Gallus gallus domesticus. There are various breeds, each serving different purposes. Some breeds are specifically bred for egg production, while others are focused on rapid growth for meat production. A young female chicken is called a pullet until she reaches one year of age, at which point she becomes a hen and typically starts laying eggs. Fully mature male chickens are referred to as roosters.

Broilers, which are chickens raised primarily for meat, are typically slaughtered around six weeks of age, preventing them from reaching the hen stage. In the case of factory farm egg layers, they reach their peak egg-laying capacity and gradually decline after about a year. Once their egg production declines significantly, these chickens are typically slaughtered. They may be used in processed chicken products or sold as soup fowl. Since they are older and more robust than pullets, they are known to enhance the flavor of soups.