A species of animal is a group of living organisms that share common characteristics and can interbreed to produce fertile offspring. Each species is classified scientifically using a two-part name, known as the binomial nomenclature, which includes the genus and species name. For example, the domestic cat is classified as Felis catus. There are millions of animal species on Earth, ranging from tiny insects to large mammals. They are categorized into various groups, such as mammals, birds, reptiles, amphibians, and fish. Each species plays a unique role in its ecosystem, contributing to biodiversity and the balance of nature.