Sand is tiny pieces of rock, coral, or shell broken down over thousands or millions of years by water, wind, and weather. If you've ever been to a beach, you've walked on millions of these tiny grains. Each grain is so small you can barely see its shape, but together they form the soft ground that shifts under your feet.

Sand forms when larger rocks get worn down by waves crashing against them, rivers tumbling them along, or desert winds blasting them. What takes nature ages to create, we use in countless ways: making concrete for buildings, creating glass for windows, and even manufacturing computer chips. Desert sand and beach sand aren't the same: desert sand grains are too round and smooth for construction, while beach sand has the rough edges that help concrete hold together.

The word also describes the color of sand, that warm tan or beige you see at many beaches. You might describe someone's hair as sand-colored or sandy if it's that light brownish-blonde shade.

When something is built on sand, it means the foundation isn't solid or reliable. If your argument for getting a pet is built on sand, it might sound good but fall apart when questioned closely.