Which of the following defines "how well" a system or product performs?

The term that encapsulates "how well" a system or product performs is quality. Quality encompasses various aspects including reliability, usability, and durability, which collectively measure a product's effectiveness in meeting user needs and expectations. It reflects the degree to which a product or system meets specified requirements and satisfies customer demands.

A system or product with high quality will consistently deliver its intended functions and performance standards, often resulting in higher user satisfaction and better overall performance. This makes quality a fundamental aspect of systems engineering, as it directly impacts both the development process and the final output.

While quantity refers to the amount or number of items produced, timeliness concerns the schedule or timing of delivery, and readiness is about the system's preparedness for use or deployment, none of these concepts directly measure the performance effectiveness or excellence of the product. Thus, quality is the most relevant term in this context.