tabby cat vs Felis catus

tabby cat and Felis catus both are nouns.

Word	Noun	Adjective	Verb	Adverb
tabby cat	Yes	No	No	No
Felis catus	Yes	No	No	No

As nouns, Felis catus is a hypernym of tabby cat; that is, Felis catus is a word with a broader meaning than tabby cat:

Other hypernyms of tabby cat include domestic cat, Felis domesticus, house cat.

tabby cat (noun)	Felis catus (noun)
a cat with a grey or tawny coat mottled with black	any domesticated member of the genus Felis