The peacock is famous for its iridescent tail feathers, which it spreads into a dramatic fan.
Strictly speaking, “peacock” refers to a male peafowl; the female is a peahen, and the species as a whole is called peafowl. The familiar bird in this question is usually the Indian peafowl, whose male has an ornate train of elongated upper-tail coverts. These feathers display large eye-like markings called ocelli, which shimmer in green, blue, bronze, and gold.
The fan is primarily used in courtship. A male raises and vibrates his train while displaying to females, producing visual movement and sometimes audible sounds. The feathers are not the bird’s actual tail feathers, though they extend beyond the shorter tail that supports them.
Another common misconception is that the colors come only from pigments. Much of the iridescence results from microscopic structures in the feathers that reflect and scatter light. Peafowl are native to South Asia, and the Indian peafowl is the national bird of India. The unrelated green peafowl and Congo peafowl also belong to the broader peafowl group.