The vireos make up a family, Vireonidae, of small to medium-sized passerine birds found in the New World and Southeast Asia. "Vireo" is a Latin word referring to a green migratory bird, perhaps the female golden oriole, possibly the European greenfinch.

A passerine is any bird of the order Passeriformes which includes more than half of all bird species. Sometimes known as perching birds, passerines generally have an anisodactyl arrangement of their toes, which facilitates perching.