IPA: /ˌæntiˈpɒpjʊlə/
KK: /æntiˈpɑp.jə.lər/
Describing something that goes against the interests or preferences of the general public.
The antipopular policies implemented by the government sparked widespread protests.
Antipopular is formed from "anti-" (meaning against) and "popular" (from Latin "popularis", meaning of the people). The word describes something that is against or not favored by the general populace.
Think of 'anti-' meaning against, and 'popular' meaning of the people — antipopular refers to something that goes against what the people like.