Gallus gallus vs hen

Gallus gallus and hen both are nouns.

Word	Noun	Adjective	Verb	Adverb
Gallus gallus	Yes	No	No	No
hen	Yes	No	No	No

As nouns, hen is a hyponym of Gallus gallus; that is, hen is a word with a more specific, narrower meaning than Gallus gallus:

Gallus gallus: a domestic fowl bred for flesh or eggs; believed to have been developed from the red jungle fowl
hen: adult female chicken

Other hyponyms of Gallus gallus include biddy, chick, cock, rooster, capon, biddy, spring chicken, Rhode Island red, Dominick, Dominique, Orpington.

Gallus gallus (noun)	hen (noun)
a jungle fowl of southeastern Asia that is considered ancestral to the domestic fowl	adult female chicken
a domestic fowl bred for flesh or eggs; believed to have been developed from the red jungle fowl	adult female bird
	female of certain aquatic animals e.g. octopus or lobster
	flesh of an older chicken suitable for stewing