A user story is a short feature description from the user's perspective using the "As a [user], I want [goal], so that [benefit]" template. It is used in agile planning to keep features grounded in customer value rather than implementation detail, and is typically accompanied by acceptance criteria that define what "done" means for the story. The format was popularized by Kent Beck and the Extreme Programming community in the late 1990s and became the dominant unit of work in Scrum and other agile frameworks.
The canonical structure has three slots: As a (the role or persona), I want (the goal or capability), so that (the benefit or business value). Example: "As a logged-in customer, I want to save items to a wishlist, so that I ...