A Sequence Diagram is a type of visual representation used in software engineering to illustrate how objects interact in a particular scenario over time. It shows the sequence of messages exchanged between different objects, represented as vertical lines, with horizontal arrows indicating the messages sent. This helps in understanding the flow of control and data in a system. These diagrams are part of the Unified Modeling Language (UML) and are particularly useful for detailing the dynamic behavior of a system. They can help developers and stakeholders visualize complex interactions, making it easier to identify potential issues and improve system design.