REST is an architectural style for distributed systems. For details please refer to the dissertation of Roy Fielding:

https://www.ics.uci.edu/~fielding/pubs/dissertation/rest_arch_style.htm

REST is also referred to as a resource-oriented architectural style and is thus opposed to the service-oriented architectural style. The World Wide Web with the Hypertext Transfer Protocol (HTTP) is the prototype of a REST architecture, whereby not every web service that is directly based on the Hypertext Transfer Protocol necessarily has to be RESTful. HTTP APIs that, for example, do not follow the hypermedial principle of REST are often referred to as REST-like APIs. In practice, almost all IOT platforms (such as Watson, Mindsphere or Predix) use a REST-like HTTP API. FORCAM FORCE Bridge supports a RESTful API with the Hypertext Application Language (HAL) but also offers plain JSON without hyperlinks.