A service relationship is defined as the cooperation between a service provider and service consumer. Service relationships are established between two or more organizations to co-create value. An organization can play the role of provider or consumer interchangeably, depending on the situation.
https://www.bmc.com/blogs/itil-key-concepts-service-management/#:~:text=and%20stakeholder%20management.-,Service%20Relationships,interchangeably%2C%20depending%20on%20the%20situation.

Organizations and people is one of the four dimensions of service management that influence the effectiveness and efficiency of service delivery1. This dimension focuses on the roles, responsibilities, and systems of authority that are needed to deliver and support services2. This dimension also covers the culture, skills, competencies, and collaboration of the people involved in service management3. Reference: ITIL Foundation - ITIL 4 Edition, page 8; ITIL 4 - A Pocket Guide, page 19; ITIL 4 Practice Guide: Organizational Change Management, page 7.