信封 (xìn fēng): envelope

I took a white envelope out of the drawer, carefully put the letter I had written inside, and then sealed it with glue.

Only the recipient's address was written on this envelope, with no sender's name, so when it was returned we had no idea who had sent it.

My mother put the New Year's money into a red envelope and quietly placed it under my pillow on New Year's Eve.

Please stick a stamp on the top right corner of each envelope, otherwise the post office won't send it for you.

He tore open the envelope and, seeing that familiar photo, suddenly thought of an old friend he hadn't been in touch with for years.