A species that is uncommon, few in number, or not abundant. A species can be rare and not necessarily be endangered or threatened, for example, an organism found only on an island or one that is naturally low in numbers because of a restricted range. Such species are, however, usually vulnerable to any exploitation, interference, or disturbance of their habitats. Species may also be common in some areas but rare in others, such as at the edge of its natural range.

"Rare" is also a designation that the IUCN—The World Conservation Union gives to certain species "with small world populations that are not at present 'endangered' or 'vulnerable' but are at risk. These species are usually localized within restricted geographical areas or habitats or are thinly scattered over a more extensive range." Some American states have also employed this category in protective legislation.