Per Wikipedia,

Service design is a form of conceptual design which involves the activity of planning and organizing people, infrastructure, communication and material components of a service in order to improve its quality and the interaction between service provider and customers.

or (my distillation)

Service design is the planning and organization of people, communications, and components involved in the interaction between service provider and customers.

• All Engineering is Design

References

• http://www.cooper.com/journal/2014/08/service-blueprints-laying-the-foundation
• https://blog.practicalservicedesign.com/the-difference-between-a-journey-map-and-a-service-blueprint-31a6e24c4a6c