Availability
Field: Security
Availability is the security property of ensuring timely and reliable access to and use of information and systems by authorized users.
Availability is one of the three properties of the CIA triad and one of the five CIANA properties. U.S. federal law defines it as “ensuring timely and reliable access to and use of information” (44 U.S.C. § 3552). It is most often discussed in terms of outages, denial-of-service attacks, and backup and recovery.
Availability and accessibility
ISO/IEC 7498-2, as quoted in NIST SP 800-160, defines availability as the “property of being accessible and usable on demand by an authorized entity.” Under that wording, a resource that is online but unusable by an authorized user, such as a document a screen reader cannot navigate, is not fully available. Rietta’s articles apply the availability property to digital accessibility on this basis.
Sources
- availability, NIST Computer Security Resource Center Glossary. Retrieved September 24, 2026.
- 44 U.S. Code § 3552, Definitions, Legal Information Institute, Cornell Law School. Retrieved September 24, 2026.