Which term refers to a system's ability to handle increased demand without impacting performance or availability?

Scalability is the term that refers to a system's ability to manage heightened demand while maintaining performance and availability. This concept is crucial for businesses and IT infrastructure as it ensures that a system can grow and adapt as user requirements change, without significant degradation in performance. A scalable system can efficiently increase its resources, such as adding more servers or bandwidth, in response to increased load.

Understanding scalability is important in various contexts, such as cloud computing and data management, where the ability to quickly adapt to varying workloads can significantly impact user experience and operational effectiveness. For example, a scalable web application can accommodate more users during peak times without affecting speed or service reliability, ultimately leading to better customer satisfaction and business continuity.

In contrast, the other terms mentioned reflect different concepts. Threshold refers to a predefined point or limit, usability pertains to how easy and user-friendly a system is, and confidential data relates to sensitive information that needs protection. Each of these terms addresses different aspects of systems and security but does not encapsulate the ability to cope with increased demand as scalability does.