Society or the public; the group of people out in the world. Can sound slightly old-fashioned depending on context.
人中での立ち振る舞いに気をつけなさいと母に言われた。
My mother told me to be careful about how I behave in public.
彼は人中での評判を気にしていた。
He was concerned about his reputation among people.
あの作家は人中を眺めるのが好きだ。
That writer likes observing people in society.