OpenAPI is a specification that allows developers to describe the functionality of their APIs in a standardized way. It provides a clear format for detailing how an API works, including the available endpoints, request methods, and response formats. This makes it easier for developers to understand and use the API without needing to dig through extensive documentation. By using OpenAPI, teams can create interactive documentation that helps users test the API directly from the documentation itself. This not only improves collaboration among developers but also enhances the overall user experience, making it simpler to integrate different services and applications.