What defines a RESTful service?

A RESTful service is defined by its adherence to REST (Representational State Transfer) architecture principles. These principles include stateless communication, the use of standard HTTP methods (such as GET, POST, PUT, DELETE), and the ability to represent resources in multiple formats (like JSON or XML). RESTful services leverage the existing standards of the web to create scalable and maintainable APIs, allowing different clients to communicate with services over the internet easily.

The other options do not relate to the core characteristics of RESTful services. For instance, synchronous communication is not a requirement of REST; RESTful services can use asynchronous patterns as well. Heavy processing is not a defining feature; rather, RESTful services prioritize lightweight interactions and efficient use of resources. Finally, a static web page does not fit the definition of a RESTful service since it typically does not involve dynamic interactions or resource manipulation commonly associated with REST APIs.