User Stories are part of an Agile approach that helps shift the focus from writing about requirements to talking about them. All Agile User Stories include a written sentence or two and, more importantly, a series of conversations about the desired functionality.
User Stories provide a light-weight approach to managing requirements for a system. User Stories are short, simple descriptions of a feature told from the perspective of the person who desires the new capability, usually a user or customer of the system. They typically follow a simple template:
As a <type of user>, I want <some goal> so that <some reason>.
User Stories are often written on index cards or sticky notes, stored in a shoe box, and arranged on walls or tables to facilitate planning and discussion. As such, they strongly shift the focus from writing about features to discussing them. In fact, these discussions are more important than whatever text is written.