The chicken (Gallus gallus domesticus) is a domesticated fowl, a subspecies of the red junglefowl. As one of the most common and widespread domestic animals, with a population of more than 24 billion in 2003, there are more chickens in the world than any other species of bird.he chicken (Gallus gallus domesticus) is a domesticated fowl, a subspecies of the red junglefowl. As one of the most common and widespread domestic animals, with a population of more than 24 billion in 2003, there are more chickens in the world than any other species of bird.