noun, noun or participle which takes 'suru', transitive verb, intransitive verb
Common for written or electronic replies (email, fax, letter). Can be used as a noun or with する as a transitive/intransitive verb.
メールの返信がまだ来ていない。
I haven't received a reply to my email yet.
彼にすぐ返信してください。
Please reply to him right away.