Service

A service is a Component of a SoftwareSystem that is relatively high-scoped and long-lived, and possibly Stateful. E.g. from the perspective of Processes in the system, a service is typically Global, accessible at some discoverable or WellKnown location (like a URL), and exists forever, preserving its State indefinitely.

Examples

The quintessential example of a service these days is arguably a web service with a REST API. But services don't need to live on the web. The filesystem on your computer is also a service by the definition above, as are other OS services like the clock and window system.