Gallus gallus vs domestic fowl

Gallus gallus and domestic fowl both are nouns.

Word	Noun	Adjective	Verb	Adverb
Gallus gallus	Yes	No	No	No
domestic fowl	Yes	No	No	No

As nouns, domestic fowl is a hypernym of Gallus gallus; that is, domestic fowl is a word with a broader meaning than Gallus gallus:

Gallus gallus: a domestic fowl bred for flesh or eggs; believed to have been developed from the red jungle fowl
domestic fowl: a domesticated gallinaceous bird thought to be descended from the red jungle fowl

Other hypernyms of Gallus gallus include fowl, poultry.

Gallus gallus (noun)	domestic fowl (noun)
a jungle fowl of southeastern Asia that is considered ancestral to the domestic fowl	a domesticated gallinaceous bird thought to be descended from the red jungle fowl
a domestic fowl bred for flesh or eggs; believed to have been developed from the red jungle fowl