Which of the following is the BEST definition of an Incident?

This describes an Alert in ITIL - a notification from a monitoring tool indicating a threshold breach, change, or failure - which is not the same as an Incident.

The official ITIL definition of an Incident is 'an unplanned interruption to an IT service or reduction in the quality of an IT service.' This definition covers both complete outages and partial degradations, and it forms the foundation of the Incident Management process in ITIL Service Operation, which focuses on restoring normal service operation as quickly as possible to minimize business impact.

This describes an Event in ITIL - a change of state that has significance for the management of a Configuration Item or IT service - which is a broader concept than an Incident.

This describes a Failure in ITIL - the loss of ability to operate to specification or deliver the required output - which is a more specific technical term distinct from the service-level definition of an Incident.