How is a service delivered between departments of same organization classified?

In ITIL, a service delivered between departments or business units within the same organization is classified as an Internal Service. Internal services are provided by an internal IT department or shared service unit to other parts of the same parent organization. This classification distinguishes them from External Services, which are delivered to customers or entities outside the organization.

External Services are those delivered to customers or organizations outside the service provider's own organization, not between departments of the same organization.

Mission Critical is a classification based on the business impact and criticality of a service, not on whether it is delivered internally or externally.

Organizational service is not a standard ITIL service classification category; the correct ITIL term for services delivered within the same organization is Internal Service.