a reply; an answer or response to a question or message (can be written or spoken).
彼の質問に対してすぐに返事をした。
I replied immediately to his question.
メールの返事がまだ来ていない。
I haven't received a reply to my email yet.
何か質問があれば遠慮なく返事をください。
If you have any questions, please don't hesitate to reply.