A disk is a flat, round object shaped like a circle or coin. The full moon looks like a bright disk in the night sky. A frisbee is a plastic disk that flies through the air when you throw it. Hockey players use a rubber disk called a puck.

In technology, disks store information for computers. A hard disk inside your computer holds all your files, photos, and programs on spinning metal disks coated with magnetic material. A CD or DVD is a type of optical disk that uses tiny marks read by a laser beam. Even though we now save files “to the cloud,” those files still live on disks somewhere in huge warehouses full of computers.

The word can also be spelled disc, especially when talking about parts of your body (like the cushioning discs between the bones in your spine) or certain kinds of music recordings. Both spellings mean the same thing, and you'll see both depending on what someone is writing about.

When something is described as disk-shaped, it means round and flat, like a pancake lying on a plate.