REST is an architectural style used in the development of Web services. REST is often preferred over SOAP (Simple Object Access Protocol) because REST uses less bandwidth, making it preferable for use over the Internet. SOAP also requires writing or using a server program and a client program.
The REST architecture and lighter weight communications between producer and consumer make REST popular for use in cloud-based APIs such as those authored by Amazon, Microsoft, and Google. When Web services using REST are called RESTful APIs or REST APIs.
REST is often used in social media sites, mobile applications and automated business processes.
REST provides advantages over leveraging SOAP. RESTful Web services are easily leveraged using most tools, including those that are free or inexpensive. REST is also much easier to scale than SOAP services. Thus, REST is often chosen as the architecture for services available via the Internet, such as Facebook and most public cloud providers. Also, development time is usually reduced using REST over SOAP.
The downside to REST is it has no direct support for generating a client from server-side-generated metadata. SOAP supports this with Web Service Description Language (WSDL).