Availability is the trust services principle that refers to the accessibility of information used by the systems, products, or services offered to a third-party provider’s customers. Trust services principles are the criteria and guidelines that are used to evaluate and report on the controls and processes of a service organization, such as a cloud service provider, a data center, or a payroll service. Trust services principles are based on the standards and frameworks issued by the American Institute of Certified Public Accountants (AICPA) and the Canadian Institute of Chartered Accountants (CICA). There are five trust services principles: security, availability, processing integrity, confidentiality, and privacy. Availability is the trust services principle that addresses the ability of the service organization to ensure that the systems, products, or services are accessible and operational for use by the customers as agreed or expected. Availability can be measured by various metrics, such as uptime, downtime, response time, recovery time, or service level agreements. References: CISSP All-in-One Exam Guide, Eighth Edition, Chapter 1: Security and Risk Management, page 20. Free daily CISSP practice questions, Question 6.