Biologists sort living things into a hierarchy of increasingly specific groups, a system that grew out of the work of Carl Linnaeus. According to the OpenStax Biology 2e textbook, the main levels, from broadest to most specific, are domain, kingdom, phylum, class, order, family, genus, and species.
All life is first divided into three domains: Bacteria, Archaea, and Eukarya. For example, the full classification of the domestic dog has eight terms: Eukarya, Animalia, Chordata, Mammalia, Carnivora, Canidae, Canis, and lupus. Scientists usually refer to a species by its two-part scientific name, the genus plus the species, such as Canis lupus.
Source: OpenStax Biology 2e, 20.1 Organizing Life on Earth
Image: Biological classification ranks, diagram by Peter Halasz (User:Pengo), public domain, via Wikimedia Commons.