What is a service?

An SOA separates partner capabilities into distinct units, or services, which are accessible over a network so users can combine and reuse them in producing applications, receiving real-time information, reporting, performing investigations, etc.

A service, in the context of information exchange, is defined as a distinct function [or unit] that allows the consumer of information to locate and access the information being provided by an information provider. Services communicate with each other by passing data from one service to another, or by coordinating an activity between two or more services.