What role do user stories have in agile software development?

User stories play a crucial role in agile software development by guiding the prioritization of development focus. Essentially, they encapsulate the needs and requirements of users in a simple, narrative format, typically structured as "As a [user], I want [goal] so that [reason]." This format emphasizes the user's perspective and helps the development team understand what features are most important to implement.

By focusing on the value that each user story brings to the user or customer, teams can make informed decisions about which features to prioritize during development iterations. This ensures that the most critical functionalities, which deliver the highest value to users, are developed and released first. This aligns with agile principles emphasizing delivering working software frequently and responding to changing requirements.

The other options, while related to aspects of software development, do not accurately capture the primary purpose of user stories. They do not serve to define test cases specifically, nor are they primarily for the purpose of project verification as formal documentation. Additionally, user stories do not inherently limit features; rather, they articulate user needs and help ensure that development focuses on delivering user value.