Definition
Service Availability is the property describing a service's ability to remain accessible and perform its required function in accordance with user and organisational requirements.
Human Explanation
A service is available when an authorised user can use it at the expected time and to the required extent.
Why it Matters
Service unavailability can interrupt operations, create financial loss and reduce the trust of customers and partners.
Conceptual Boundary
Service Availability describes an outcome or property. It is not the same as Fault Tolerance or High Availability, which are architectural capabilities and approaches used to support that outcome.
Practical Perspective
The required level of availability should follow the service's importance, usage pattern and disruption impact rather than an assumption that every service must remain continuously available.