What refers to the extent to which a solution is operable and accessible when required?

The term that refers to the extent to which a solution is operable and accessible when required is "availability." Availability is a key aspect of system performance, indicating the degree to which a system is ready for use at any given moment. In this context, it focuses on the accessibility of a system for users or stakeholders whenever they need to engage with it.

When discussing system requirements or performance metrics, availability ensures that users can depend on the system to be operational when necessary, which is crucial for maintaining effective business operations and user satisfaction. Factors that influence availability include system downtime, maintenance schedules, and the capability of the system to recover from failures.

In contrast, scalability refers to a system's ability to handle increasing loads or expand as demand grows, usability focuses on how user-friendly and intuitive a system is for end users, and reliability is about the consistency and dependability of a system over time. While all these aspects contribute to the overall quality of a solution, availability specifically addresses the critical issue of being operational and accessible when required.