Dust is the fine, powdery layer of tiny particles that settles on surfaces everywhere. It's made up of countless microscopic bits: dead skin cells, pollen, fabric fibers, dirt tracked in from outside, and even tiny fragments of meteors that have burned up in Earth's atmosphere. If you run your finger across a bookshelf you haven't cleaned in a while, that gray coating on your fingertip is dust.

Dust appears constantly because these tiny particles float through the air and eventually drift downward, coating tables, floors, and windowsills. Even in the cleanest homes, dust accumulates within days. Some people are allergic to dust, or more precisely, to dust mites (microscopic creatures that live in dust and feed on shed skin cells).

The word also means to clean by removing dust, usually by wiping surfaces with a cloth. When you dust the furniture, you're clearing away that powdery layer.

Dust can also describe anything reduced to fine particles. After a building is demolished, workers clear away the dust and rubble. The phrase bite the dust means to fail or be defeated. And when something hasn't been used in forever, people say it's gathering dust, like that board game in your closet you've forgotten about.