The term used to describe major classification groups of organisms is taxon (plural: taxa).

Here's a breakdown of the taxonomic hierarchy:

* Domain: The broadest category (e.g., Bacteria, Archaea, Eukarya)

* Kingdom: A large group of related phyla (e.g., Animalia, Plantae)

* Phylum: A large group of related classes (e.g., Chordata, Arthropoda)

* Class: A large group of related orders (e.g., Mammalia, Aves)

* Order: A large group of related families (e.g., Primates, Carnivora)

* Family: A group of related genera (e.g., Hominidae, Felidae)

* Genus: A group of closely related species (e.g., Homo, Panthera)

* Species: The basic unit of classification (e.g., Homo sapiens, Panthera leo)

Each of these levels of classification represents a taxon.