photo op vs social affair

photo op and social affair both are nouns.

Word	Noun	Adjective	Verb	Adverb
photo op	Yes	No	No	No
social affair	Yes	No	No	No

As nouns, social affair is a hypernym of photo op; that is, social affair is a word with a broader meaning than photo op:

photo op: an occasion that lends itself to (or is deliberately arranged for) taking photographs that provide favorable publicity for those who are photographed
social affair: a formal or official social gathering or ceremony of people

Other hypernyms of photo op include affair, function, occasion, social function, social gathering, social occasion.

photo op (noun)	social affair (noun)
an occasion that lends itself to (or is deliberately arranged for) taking photographs that provide favorable publicity for those who are photographed	a formal or official social gathering or ceremony of people