Someone else's affairs; an issue or matter that is treated as not one's own problem — used to indicate detachment or lack of concern ('as if it's someone else's problem').
彼は他人事のように話した。
He spoke as if it were someone else's problem.
会社の倒産ニュースを聞いても、彼にとっては人事だ。
Even hearing the company's bankruptcy news, for him it's someone else's problem.
その問題を他人事として片付けてはいけない。
You shouldn't treat that issue like someone else's problem.