school bus vs passenger vehicle

school bus and passenger vehicle both are nouns.

Word	Noun	Adjective	Verb	Adverb
school bus	Yes	No	No	No
passenger vehicle	Yes	No	No	No

As nouns, passenger vehicle is a hypernym of school bus; that is, passenger vehicle is a word with a broader meaning than school bus:

school bus: a bus used to transport children to or from school
passenger vehicle: a vehicle carrying many passengers; used for public transport

Other hypernyms of school bus include autobus, bus, charabanc, coach, double-decker, jitney, motorbus, motorcoach, omnibus.

school bus (noun)	passenger vehicle (noun)
a bus used to transport children to or from school	a vehicle carrying many passengers; used for public transport