Are domain services part of domain model?

Are services part of domain model according to DDD? If we google for "ddd onion architecture", we can mostly see that the most inner layer is called something like "Domain Model Layer" and the second is "Domain Services", for example, [dead link, NSFW anymore] . But in https://en.wikipedia.org/wiki/Domain-driven_design and DDD book we see that that entities, value objects and services all express the model and are model elements. If entities, value objects and services are all part of domain model, how should we call those two layers of onion: model (entities + value objects) and services (as I sometimes do)? But if all are part of domain model, this naming does not seem accurate.