codify the creation of value
Services are a means to codify the creation of value for the business. Typically a service is a component of a larger system, modeled as a series of steps, a boundary delimited fragment, where each step is a key waypoint on the road toward some definite objective.
Being a mental model, there is no single definite solution. The “right” model of a service is one that produces value for the business under the current circumstances of time and place.