A raven is one of several larger-bodied species of the genus Corvus. These species do not form a single taxonomic group within the genus.
There is no consistent distinction between “crows” and “ravens”, and these appellations have been assigned to different species chiefly on the basis of their size, crows generally being smaller than ravens.
The largest raven species are the common raven and the thick-billed raven.
The term “raven” originally referred to the common raven, the type species of the genus Corvus, which has a larger distribution than any other species of Corvus, ranging over much of the Northern Hemisphere.
The modern English word raven has cognates in all other Germanic languages, including Old Norse (and subsequently modern Icelandic) hrafn and Old High German (h)raban, all of which descend from Proto-Germanic *hrabanaz.
Collective nouns for a group of ravens (or at least the common raven) include “unkindness”, “treachery”, and “conspiracy”. In practice, most people use the more generic “flock”.
The common raven (Corvus corax), also known as the northern raven, is a large all-black passerine bird. Found across the Northern Hemisphere, it is the most widely distributed of all corvids. There are at least eight subspecies with little variation in appearance, although recent research has demonstrated significant genetic differences among populations from various regions. It is one of the two largest corvids, alongside the thick-billed raven, and is possibly the heaviest passerine bird; at maturity, the common raven averages 63 centimetres (25 inches) in length and 1.2 kilograms (2.6 pounds) in mass. Common ravens can live up to 21 years in the wild, a lifespan surpassed among passerines by only a few Australasian species such as the satin bowerbird and probably the lyrebirds. Young birds may travel in flocks but later mate for life, with each mated pair defending a territory.