Genus

(Plural: genera). The division of classification into a family is divided and which has one or more species, i.e. the rank below a family, descended from a common ancestor. A genus is made up of a group of structurally or phylogenetically related species

A genus that contains a single species is known as monotypic

For example, bluebirds are in the genus Sialia and the fairy-bluebirds are in the genus Irena.