Emission is the act of sending something out or releasing it, or the thing that gets released. The word most commonly describes gases, particles, or energy that flow out from a source into the surrounding environment.

When a car's engine burns gasoline, it produces carbon dioxide emissions that exit through the tailpipe. When a factory operates, it might release emissions into the air from its smokestacks. Scientists measure these emissions to understand how human activities affect air quality and climate.

A light bulb produces light emissions. A radio tower creates radio emissions. Your own body produces heat emissions (which is why you feel warm).

While emission usually refers to physical substances or energy, it can occasionally describe other things being sent out or released. A government might authorize the emission of new currency, meaning it releases new money into circulation.

The related verb is emit. A volcano emits ash and gases. A phone screen emits blue light. Whenever something releases or sends something outward, it emits it, and what comes out is an emission.