quiz vs pop quiz

quiz and pop quiz both are nouns.

Word	Noun	Adjective	Verb	Adverb
quiz	Yes	No	Yes	No
pop quiz	Yes	No	No	No

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

quiz (noun)	pop quiz (noun)
an examination consisting of a few short questions	a quiz given without prior warning

quiz (verb)	pop quiz (verb)
examine someone's knowledge of something