pizza vs sausage pizza

pizza and sausage pizza both are nouns.

Word	Noun	Adjective	Verb	Adverb
pizza	Yes	No	No	No
sausage pizza	Yes	No	No	No

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

pizza: Italian open pie made of thin bread dough spread with a spiced mixture of e.g. tomato sauce and cheese
sausage pizza: tomato and cheese pizza with sausage

Other hyponyms of pizza include pepperoni pizza, cheese pizza, anchovy pizza, Sicilian pizza.

pizza (noun)	sausage pizza (noun)
Italian open pie made of thin bread dough spread with a spiced mixture of e.g. tomato sauce and cheese	tomato and cheese pizza with sausage