A Use Case Diagram is a visual representation that illustrates the interactions between users, known as actors, and a system. It helps to identify the various ways users can interact with the system to achieve specific goals, known as use cases. This diagram is commonly used in software development to clarify requirements and ensure that all user needs are considered. In a Use Case Diagram, actors are depicted as stick figures, while use cases are represented as ovals. Lines connect actors to their respective use cases, showing the relationships and interactions. This diagram serves as a valuable tool for stakeholders, including developers and project managers, to understand system functionality and user requirements.