A Web Service is a software system designed to support interoperable machine-to-machine interaction over a network.

Many organizations use multiple software systems for management. Different software systems often need to exchange data with each other, and a web service is a method of communication that allows two software systems to exchange this data over the internet. The software system that requests data is called a service requester or consumer, whereas the software system that would process the request and provide the data is called a service provider or producer.

Different software might be built using different programming languages, and hence there is a need for a method of data exchange that doesn't depend upon a particular programming language. Most types of software can, however, interpret XML or JSON tags. Thus, web services can use XML or JSON files for data exchange.

Two predominant web services frameworks, REST and SOAP, are used in web site development.

REST (Representational State Transfer) and SOAP (Simple Object Access Protocol) provide mechanisms for requesting information from resources, REST, or from endpoints, SOAP. Perhaps the best way to think of these technologies is as a method of making a remote procedure call against a well-defined API. SOAP has a more formal definition mechanism called WSDL, Web Services Definition Language, and is more complex to implement. REST uses the standard HTTP request and response mechanism, simplifying implementation and providing for a more flexible, loose coupling of the client and server. Note that REST also supports the transfer of non-XML messages such as JSON (JavaScript Object Notation).