Service vs Process
A service is the bundling or packeting of something that is consumed by someone and there is a provider which take responsibility in delivering it according to some kind of agreement.
The service might consists of multiple parts/options where some can be mandatory and others can be optional. Sometimes the service is static and can only be purchased in its current shape but nevertheless, the consumer needs and wants it.
A process is the way (a sequence of activities) where a defined output is achieved.
Its supposed to be efficient and repeatable so that the output is achieved every time the process is triggered and completed.
The service is consumed once or frequently over time.
The process is triggered and driven according to the flow.