A decorated paper envelope or bag used to put cash gifts or small presents in; commonly used for celebrations (e.g., weddings) — also called a noshibukuro.
結婚式には白いのし袋にご祝儀を入れて渡す。
For a wedding, you put the gift money in a white noshi envelope and give it.
コンビニでのし袋を買って親戚に包むお金を用意した。
I bought a noshi envelope at the convenience store and prepared the money to give to relatives.
のし袋には名前と金額を丁寧に書いておくと失礼がない。
It's polite to write your name and the amount neatly on the noshi envelope.