Availability is the security principle that ensures data and services are accessible to authorized users when needed.
Availability is one part of the widely used CIA triad in information security. The other two elements are confidentiality, which limits information access, and integrity, which protects information from unauthorized alteration. Together, the three principles provide a compact way to discuss core security goals.
Organizations support availability through backups, redundancy, disaster recovery, capacity planning, monitoring, and resistance to denial-of-service attacks. A system can be confidential and accurate yet still fail its users if it is unreachable during an important operation.
Availability does not mean that every person can access everything. Access remains controlled by authorization policies; the principle concerns reliable access for permitted users and processes.