A service is a discrete, independently deployable unit of functionality that exposes a well-defined interface, allowing clients and other components to invoke its capabilities without knowledge of its internal implementation. In an n-tier architecture, services typically reside in the middle or application tier, encapsulating business logic and mediating between client-facing presentation layers and back-end data storage. See https://namazustudios.com/docs/general-concepts/n-tier-architecture/ for details.