populism vs school of thought

populism and school of thought both are nouns.

Word	Noun	Adjective	Verb	Adverb
populism	Yes	No	No	No
school of thought	Yes	No	No	No

As nouns, school of thought is a hypernym of populism; that is, school of thought is a word with a broader meaning than populism:

populism: the political doctrine that supports the rights and powers of the common people in their struggle with the privileged elite
school of thought: a belief (or system of beliefs) accepted as authoritative by some group or school

Other hypernyms of populism include doctrine, ism, philosophical system, philosophy.

populism (noun)	school of thought (noun)
the political doctrine that supports the rights and powers of the common people in their struggle with the privileged elite	a belief (or system of beliefs) accepted as authoritative by some group or school