SOAP is a way for a program running in one kind of operating system to communicate with a progam in the same or another kind of an operating system by using the World Wide Web's Hypertext Transfer Protocoland its Extensible Markup Language as the mechanisms for information exchange.

While REST stands for Representational State Transfer, which is an architectural style for networked hypermedia applications, it is primarily used to build Web services that are lightweight, maintainable, and scalable.