Equipment is an artifact subtype whose cards can be attached to creatures to grant additional abilities or bonuses. Unlike Auras, Equipment normally remains on the battlefield if the creature carrying it leaves, allowing another creature to pick it up later.
Stoneforge Mystic can search for Equipment and help put it onto the battlefield, Puresteel Paladin combines Equipment with card advantage, and Sigarda's Aid makes attaching a freshly cast piece of Equipment considerably more efficient.