A web service is a method of communication between two electronic devices (machine-to-machine interaction) over a network (e.g.: the World Wide Web).
A web service is an application that responds to requests using a protocol built on top of HTTP (see also http), the protocol of the World Wide Web. The term can also designate the application protocol itself.
Some web services follow the REST (representational state transfer - see also rest) principle, where communication takes the form of requests from a client and matching responses from the server, and the server does not keep track of successive requests from a client (no sessions).