what people say; gossip; rumors
Refers to public talk, gossip, or rumors circulating in society. Often used in contexts about reputation or what others might say.
People will talk, so let's be careful about our actions.
That incident is a topic that easily becomes the talk of the town.
評判 is reputation or public estimation, often with a positive or negative evaluation, whereas 世間の口 is neutral talk or gossip itself.
A set phrase combining 世間 (society, the world of people) and 口 (mouth), literally 'the mouth of society', meaning public talk or gossip.