Which part of the CIA triad refers to the accessibility of information when needed?

The correct choice highlights the concept of "Availability" within the CIA triad, which is a foundational model for information security. Availability refers to the assurance that information and resources are accessible to authorized users when they need them. This means that systems, data, and services must be operational and functional, allowing users to access necessary information without interruption.

In practical terms, ensuring availability involves implementing measures such as redundancy, failover systems, and regular maintenance to prevent downtime. It also could include tactical planning for disaster recovery to ensure that information can be accessed even in adverse conditions. Thus, the focus is on minimizing service interruptions and ensuring that information can be retrieved as required, maintaining operational continuity and efficiency.