“If you are in an agency or consultancy environment, you might categorise service design as part of user experience and/or experience strategy. If you come from a product environment, service design might vibrate more to what you consider as product management and business design. In a nutshell, service design is delivering a designed experience onto different levels of actors with a more holistic approach in mind. Let me elaborate on that.”
Explaining it to UX designers is one thing, to your mother is another.