Service
Here's a definition I tend to use:
A service is a self-contained, repeatable task with a described service interface and is an atomic unit of functionality in service-oriented architecture. A service can be reused by multiple applications. A service's functionality is independent of the computing platform on which it runs, and can be validated through testing. (Best practice: A service should be designed as a context-free service.)
The technical aspects of a service can best be described by a service contract, which includes not just service interface but the service behavior as well (plus other aspects).
