Telephone is a device that lets people talk to each other across distances by converting voices into electrical signals that travel through wires or, in modern cell phones, through the air as radio waves. When you speak into a telephone, your voice vibrations become electrical pulses that zip to another telephone, where they're converted back into sound.

Alexander Graham Bell invented the telephone in 1876, and it revolutionized human communication. Before the telephone, if you wanted to talk to someone far away, you had to write a letter and wait days or weeks for a reply, or travel to see them in person. The telephone made instant long-distance conversation possible.

For most of the 20th century, telephones were connected by physical wires to wall jacks in homes and offices. Today, most people carry cell phones (also called mobile phones or smartphones) that work wirelessly and do much more than just make calls.

When someone asks for your telephone number, they want the unique set of digits that will connect a call to your phone. To telephone someone means to call them: “I'll telephone you after dinner to discuss our science project.”