The word "quetzal" was originally used for just the Resplendent Quetzal, Pharomachrus mocinno, the famous long-tailed quetzal of Central America, which is the national bird of Guatemala. It still often refers to that bird specifically but now also names all the species of the genera Pharomachrus and Euptilotis. The six quetzal species and their English common names are:
Euptilotis neoxenus is related to Pharomachrus and is called the Eared Quetzal by some authorities, such as the American Ornithologists' Union, but the Eared Trogon by others.
Pharomachrus is from ancient Greek pharos, "mantle", and makros, "long", referring to the wing and tail coverts of the Resplendent Quetzal. (The second h is unexplained.)