public opinion vs popular opinion

public opinion and popular opinion both are nouns.

Word	Noun	Adjective	Verb	Adverb
public opinion	Yes	No	No	No
popular opinion	Yes	No	No	No

As nouns, public opinion and popular opinion are synonyms defined as:

public opinion and popular opinion: a belief or sentiment shared by most people; the voice of the people

Other synonyms of public opinion include opinion, vox populi.

public opinion (noun)	popular opinion (noun)
a belief or sentiment shared by most people; the voice of the people	a belief or sentiment shared by most people; the voice of the people