A State Transition Diagram is a visual representation used in systems design to illustrate how an object or system transitions between different states. Each state represents a specific condition or situation of the system, while arrows indicate the transitions triggered by events or conditions. This diagram helps in understanding the behavior of systems, especially in software engineering and control systems. These diagrams are particularly useful in modeling the lifecycle of an object, such as a software application or a machine. By clearly showing the possible states and transitions, they aid developers and engineers in designing, analyzing, and implementing systems effectively.