A washer is a small flat ring, usually made of metal, rubber, or plastic, that goes under a bolt or nut to help distribute pressure and prevent damage. When you tighten a bolt through wood or metal, the washer spreads out the force so the bolt head doesn't dig into the surface or crack it. Think of it like putting a coaster under a glass to protect a table: the washer protects the material you're fastening together.

Washers also help keep bolts from loosening over time. The washer creates friction and acts as a barrier, making it harder for vibrations to shake the bolt loose. You'll find washers in bicycles, furniture, playground equipment, and almost anything held together with bolts.

The word also refers to a washing machine, the appliance that cleans clothes. When someone says they need to run a load in the washer, they mean the washing machine. Some people call the machine that dries clothes a dryer and the one that washes them a washer to keep the names straight.