Domain Services are part of the Domain Model

Typically, Aggregate methods act as the entry points to application logic - they handle both data and behavior. Domain Services contain business logic that doesn't fit clearly inside a Domain element, like an Aggregate, Entity, or Value Object. They are introduced on a case-by-case basis and avoided by default.

Domain Services, like other elements in the Domain Layer, deal in the world of pure objects or functions, without the knowledge of the external world or technology implementations.