Trinomial nomenclature

In biology, trinomial nomenclature refers to names for taxa below the rank of species. This is different for animals and plants:
 * for animals see trinomen. There is only one rank allowed below the rank of species: subspecies.
 * for plants see ternary name. There is an indeterminate number of infraspecific ranks allowed below the level of species: subspecies is the highest ranked of these.

Word origin
Latin. Literally meaning a three-term naming system.