What does the large rectangular box separating use cases from actors represent on a use case diagram?

The large rectangular box in a use case diagram represents the system boundary. This boundary defines the scope of the system being analyzed or developed, delineating what is inside the system (the use cases) from what is outside of it (the actors). Actors are external entities such as users, other systems, or organizations that interact with the system, and the use cases describe the specific functionalities the system will provide in response to those interactions.

Establishing a clear system boundary is crucial in business analysis, as it helps stakeholders understand what is included in the project and what is not. It aids in managing expectations and defining the limits of the system’s capabilities, ensuring that the analysis focuses on the right areas without introducing irrelevant elements. In this way, the system boundary serves as a fundamental aspect of modeling the system's interactions and requirements effectively.