Core and Supplementary Services

A core service is simply the fundamental service that the service is providing. A supplementary service is anything that could be considered an extra on top of that basic service. 

So for example, for a hotel, the core service would be providing a bed. The supplementary services are the services that add to that core experience. 

Supplementary services could include laundry services, business services, conference facilities, dining room, gymnasium, pool, mini-golf, vending machines, bar and so on. 

Defining what is core and supplementary can be difficult for many services as what might be considered supplementary comes to be considered core (e.g. McDonald's cafes were supplementary and are now a core part of their service). 

Services can also innovate around this idea by providing extra services or even stripping down service to its bare essentials. E.g. the Japanese capsule hotels - see below.