What is defined as the ability of a service, component or configuration item (CI) to perform its agreed function when required?

Serviceability refers to the contractual commitment by a third-party supplier to maintain or repair a component within agreed terms, not the ability to perform an agreed function.

Availability is formally defined in ITIL as the ability of a service, component, or CI to perform its agreed function when required. It is expressed as a percentage of agreed service time and is managed through availability management, which ensures services meet both current and future agreed availability targets.

Capacity describes the maximum throughput or workload a service or component can handle, not its ability to be available when needed.

Continuity (IT Service Continuity) relates to ensuring services can recover and continue after a major disruption or disaster, not to normal operational availability.