Trigger originally meant the small lever you pull to fire a gun. When you squeeze the trigger, it releases the mechanism that makes the gun shoot.

Today, trigger has several related meanings. Something that triggers an event causes it to start suddenly, like flipping a switch. A smoke alarm is triggered by detecting smoke particles in the air. A burglar alarm might be triggered when someone opens a window. In science, researchers study what triggers earthquakes or volcanic eruptions.

In everyday conversation, people often say something triggered a memory or emotion, meaning it brought that feeling or thought rushing back unexpectedly. Smelling cookies baking might trigger memories of visiting your grandmother's house. Hearing a certain song could trigger feelings of happiness from a great vacation.

The word suggests something sudden and automatic, like a chain reaction starting. When something is triggered, it happens quickly, almost like a switch being flipped. A single spark can trigger a forest fire. One student laughing might trigger the whole class to start giggling. Understanding what triggers certain reactions helps us predict and prepare for what might happen next.