A Use Case Diagram is a visual representation that illustrates how different users, known as actors, interact with a system. It helps to identify the various functionalities or use cases that the system offers. By showing the relationships between actors and use cases, these diagrams provide a clear overview of what the system does and who benefits from it. These diagrams are particularly useful in the early stages of software development, as they help stakeholders understand requirements and expectations. By mapping out interactions, Use Case Diagrams facilitate better communication among team members, ensuring everyone is on the same page regarding the system's capabilities.