Signal is a way of sending a message or information, especially when you can't use regular speech. When a baseball coach touches his cap, then his ear, then his belt, those movements are signals telling the batter and runners what play to run. When a ship flashes its lights in a pattern at night, it's signaling to other vessels. Traffic lights use colored signals to tell drivers when to stop and go.

Signals work because the sender and receiver agree on what each signal means ahead of time. Ancient Romans used smoke signals to send messages across long distances. Today, your phone receives invisible radio signals from cell towers. Your brain sends electrical signals through your nerves to make your muscles move.

The word also means to show or indicate something, often without speaking. When dark clouds signal an approaching storm, they're giving you information. If your friend signals their approval with a thumbs up, you know they agree.

In some contexts, a signal can mean anything that stands out from background noise or confusion. Scientists search for signals from space that might indicate intelligent life. A detective looks for signals in the evidence, clues that point toward the truth. When something gives you a clear signal, it's telling you something important and worth paying attention to.