A piece of work written from the user's point of view, usually in the format 'As a [user], I want [thing], so that [reason].'
Example: 'As a shopper, I want to save items to a wishlist, so that I can buy them later.'
In practice: The format is meant to keep focus on user value instead of just technical tasks. Teams that write stories as 'As a developer, I want to refactor X' have basically abandoned the point of the format.