What is an Incident
An incident is an unplanned disruption or degradation of service.
Based on the definition provided, an incident is something that needs to be resolved immediately. This can either be through a permanent fix, a workaround or a temporary fix. An example of an incident would be a server crash which causes a disruption in the business process. If a server is used only during office hours, a crash after office hours is, strictly speaking based on the definition, not yet an incident since the no service was affected. It becomes an incident only when the outage extends to the hours of use.
If a disruption is planned, for example, a scheduled maintenance, this is not an incident. The outage should not be counted as part of the unavailability. If the scheduled outage exceeds the planned schedule, then the over time for the outage becomes an incident.
If an incident requires changes the emergency change process is normally followed, specially if the service level is critical