A compressor is a machine that squeezes air or gas into a smaller space, making it denser and often storing it under pressure. Think of it like squeezing a sponge: you force something into less room than it naturally wants to occupy.

Air compressors power all kinds of tools, from the nail guns that construction workers use to build houses to the air wrenches mechanics use to remove car tires quickly. The compressor squeezes air into a tank, building up pressure like blowing up a balloon. When you pull the trigger on a pneumatic tool, that pressurized air rushes out with enough force to drive nails through wood or spin bolts loose.

You encounter compressors more often than you might realize. Refrigerators and air conditioners use compressors to squeeze and move refrigerant, the special gas that makes things cold. Scuba tanks are filled using powerful compressors that pack enough air into a small tank to let divers breathe underwater.

The word can also describe something that makes digital files smaller. A file compressor squeezes data so it takes up less space on your computer, just like the machine squeezes air into less space. When you compress a photo to email it, you're making the file smaller so it sends faster.