In agile development, a user story serves as a brief description of a feature from the perspective of the end user. Its main purpose is to capture the user's needs and expectations, facilitating communication among team members and stakeholders. User stories help prioritize features in the backlog, enabling teams to focus on delivering value incrementally. By detailing who the user is, what they need, and why it matters, user stories promote collaboration and ensure that the final product aligns with user expectations and real-world applications.