Web service is a standardized medium to propagate communication between the client and server applications on the World Wide Web.
A web service is a software module which is designed to perform a certain set of tasks.
The web services can be searched for over the network and can also be invoked accordingly.
When invoked the web service would be able to provide the functionality to the client which invokes that web service.
The main component of a web service is the data which is transferred between the client and the server, and that is XML or JSON.