1A person other than oneself — other people in general, as distinct from oneself.
他人の意見にもきちんと耳を傾けるべきだ。
You should listen carefully to other people's opinions too.
彼は他人と比べてばかりで疲れているようだ。
He seems tired from constantly comparing himself to others.
これはあくまで他人の問題であって、私には関係ない。
This is entirely someone else's problem — it has nothing to do with me.
他人を思いやる気持ちを大切にしよう。
Let's cherish the feeling of caring for other people.
2A person unrelated by blood — someone outside one's family, sometimes emphasized as a complete stranger with the phrase 赤の他人.
養子とはいえ、法律上はもう他人ではない。
Even though he's adopted, legally he's no longer unrelated.
隣に住んでいるのは赤の他人だが、とても親切だ。
The person living next door is a complete stranger, yet very kind.
遺産は他人に渡り、親族には何も残らなかった。
The inheritance went to an unrelated person, and nothing was left for the relatives.
3Someone who doesn't belong to a particular group or circle — an outsider.
転校生は最初、クラスで他人のように扱われた。
At first, the transfer student was treated like an outsider in the class.
そんなに他人行儀にしなくてもいいよ。
You don't have to be so formal with me, you know.
長年一緒にいたのに、急に他人のように感じられた。
Even though we'd been together for years, he suddenly felt like a stranger.