There are always two words in the scientific name. The first (generic) is the name of the genus to which the animal belongs. The second is its trivial name. Together, the genus and trivial names make up the complete name of a "species." Generally speaking, the term "species" is used to differentiate groups of organisms that theoretically cannot interbreed. In the main, however, species separation is based on morphological characteristics. "Genus" is the smallest organizational grouping for one or more closely-related species.