Which term is defined as a shared boundary between functional units?

The term that refers to a shared boundary between functional units is "interface." In systems engineering, an interface is critical as it defines how different parts or components of a system interact and communicate with one another. It encompasses the points of contact and the means of exchange between these functional units, including data, signals, and physical connections.

Understanding interfaces is essential for ensuring that integrated systems work cohesively. They set the standards for interactions, facilitating clarity in how components will work together. Proper interface definition helps reduce risks during integration and contributes to the overall functionality and performance of a system.

In contrast, integration focuses on the process of combining components into a functioning whole, whereas boundary conditions typically refer to specific constraints or limits that influence how a system behaves at its edges. Constraints might dictate certain restrictions on design or performance but do not inherently describe the interaction points between functional units.