A user story is similar to a PBI, but it goes beyond a specific change or requirement. It puts the end-user and their experience front and center. It’s the smallest unit of work in agile development, expressed from the user’s perspective. This is a functional increment that’s expected to contribute to the value of the overall product.
While this term may make it sound like this is a lengthy way to describe needs and requests, that couldn’t be further from reality. User stories should actually fit together more like a puzzle. You should be able to schedule and plan for each piece.