Defining the processes needed to operate a new service is part of:

Service Design includes a dedicated activity - 'Design the processes' - which covers identifying, defining, and documenting all processes required to deliver and manage the new service. This ensures operational procedures are planned and documented before the service moves into Service Transition and Service Operation, avoiding gaps in process coverage.

Service Strategy is focused on understanding market needs, defining service offerings, and developing strategy - not on the detailed design of operational processes for a specific service.

Service Transition focuses on planning and executing the deployment of a service into the live environment, not on defining what processes are needed to run the service.

IT Operations Management within Service Operation executes operational activities day-to-day but does not define the processes required for a new service - that definition belongs in Service Design.