for reply; for a response
Used as a modifier, often in phrases like 返信用封筒 (reply envelope) or 返信用はがき (reply postcard).
返信用の封筒を同封してください。
Please enclose a reply envelope.
返信用はがきに必要事項を記入する。
Fill in the required information on the reply postcard.
self-addressed stamped envelope; SASE
reply postcard; international reply coupon
self-addressed stamped envelope; SASE
Compound of 返信 (reply) + 用 (for the purpose of).