A peacock is called a peacock because it is the male bird. The female, strictly speaking, should be referred to as the peahen. Peacock in common usage has become a generic term to encompass any pheasant-like bird with a long showy tail that can be spread out like a fan.
These birds should, more accurately, be referred to as peafowl.
These birds should, more accurately, be referred to as peafowl.