A Requirements Document is a formal document that outlines the specific needs and expectations for a project or system. It serves as a guide for developers, stakeholders, and project managers, detailing what the final product should achieve. This document typically includes functional requirements, non-functional requirements, and any constraints that may affect the project. The purpose of a Requirements Document is to ensure that all parties involved have a clear understanding of the project goals. By providing a comprehensive overview, it helps prevent misunderstandings and scope creep, ultimately leading to a more successful outcome for the project.