A web service (WS) is either:

• a service offered by an electronic device to another electronic device, communicating with each other via the Internet, or
• a server running on a computer device, listening for requests at a particular port over a network, serving web documents (HTTP, JSON, XML, images).

The use of the term "Web" in Web Service is a misnomer. Web Services do not use the World Wide Web (WWW), a human user interface running on the Internet, but rather a machine-to-machine service running on the Internet using the WWW protocols.

In a web service, a web technology such as HTTP is used for transferring machine-readable file formats such as XML and JSON.

In practice, a web service commonly provides an object-oriented web-based interface to a database server, utilized for example by another web server, or by a mobile app, that provides a user interface to the end-user. Many organizations that provide data in formatted HTML pages will also provide that data on their server as XML or JSON, often through a Web service to allow syndication. Another application offered to the end-user may be a mashup, where a Web server consumes several Web services at different machines and compiles the content into one user interface.