A sender is the person or thing that sends something to someone else. When you mail a birthday card to your grandmother, you're the sender and she's the receiver. The return address on an envelope shows who the sender is, in case the letter needs to be sent back.

In everyday conversation, we use sender most often when talking about mail, packages, emails, and text messages. Your email program shows you the sender's name so you know who wrote to you. A mysterious package might make you curious about its sender.

The word also applies beyond mail and messages. In communication, the sender is whoever originates a message, whether they're speaking, writing, or even using hand signals. A teacher explaining a math problem is the sender of information, while students listening are the receivers.

Sometimes people talk about “return to sender,” which means sending mail back to whoever sent it, usually because it couldn't be delivered to the intended recipient. You might write “return to sender” on an envelope addressed to someone who doesn't live at your house anymore.