porch vs back porch

porch and back porch both are nouns.

Word	Noun	Adjective	Verb	Adverb
porch	Yes	No	No	No
back porch	Yes	No	No	No

As nouns, back porch is a hyponym of porch; that is, back porch is a word with a more specific, narrower meaning than porch:

porch: a structure attached to the exterior of a building often forming a covered entrance
back porch: a porch for the back door

Other hyponyms of porch include deck, front porch, portico, stoep, stoop, gallery, veranda, verandah.

porch (noun)	back porch (noun)
a structure attached to the exterior of a building often forming a covered entrance	a porch for the back door