A web service is an interoperable application that can be delivered over the web. These are also commonly known as application services. Characteristics of web services include the interoperable nature between the applications over a network, and the ability to communicate with other services, as depicted in the following diagram:
These applications can interact with each other, irrespective of the underlying technology used for building them. These application services provide the output that other applications can understand, and the output of an application is consumable by another application.
In short, a service is referred to as a web service when it is platform independent, involves interaction with other services, and communicates over the web.
