A passerine is a bird of the order Passeriformes, which includes more than half of all bird species. Sometimes known as perching birds or, less accurately, as songbirds, the passerines form one of the most diverse terrestrial vertebrate orders; with over 5,000 identified species, it has roughly twice as many species as the largest of the mammal orders, the Rodentia. It contains more than 110 families, the second most of any order of vertebrates (after the Perciformes).
The names "passerines" and "Passeriformes" are derived from Passer domesticus, the scientific name of the eponymous species (the House Sparrow) and ultimately from the Latin term passer for Passer sparrows and similar small birds.
The order is divided into three suborders, Tyranni (suboscines), Passeri (oscines), and the basal Acanthisitti. Oscines have the best control of their syrinx muscles among birds, producing a wide range of songs and other vocalizations (though some of them, such as the crows, do not sound musical to human beings); some such as the lyrebird are accomplished imitators. The Acanthisittids or New Zealand wrens are tiny birds restricted to New Zealand, at least in modern times; they were long placed in Passeri; their taxonomic position is uncertain, although they seem to be a distinct and very ancient group.
Most passerines are smaller than typical members of other avian orders. The heaviest and altogether largest passerines are the Thick-billed Raven and the larger races of Common Raven, each exceeding 1.5 kg (3.3 lb) and 70 cm (28 in). The Superb Lyrebird and some birds-of-paradise, due to very long tails or tail coverts, are longer overall. The smallest passerine is the Short-tailed Pygmy-Tyrant, at 6.5 cm (2.6 in) and 4.2 g (0.15 oz).