way of providing interoperability between computer systems on the Internet. REST-compliant Web services allow requesting systems to access and manipulate textual representations of Web resources using a uniform and predefined set of stateless operations. https://en.wikipedia.org/wiki/Representational_state_transfer
converted to JSON, and returned to the client. This allows you to return basically any form of data. https://developer.wordpress.org/rest-api/extending-the-rest-api/adding-custom-endpoints/#return-value
the object: $param = $request['some_param']; // Or via the helper method: $param = $request->get_param( 'some_param' ); // You can get the combined, merged set of parameters: $parameters = $request->get_params(); // The individual sets of parameters are also available, if needed: $parameters = $request->get_url_params(); $parameters = $request->get_query_params(); $parameters = $request->get_body_params(); $parameters = $request->get_json_params(); $parameters = $request->get_default_params(); // Uploads aren't merged in, but can be accessed separately: $parameters = $request->get_file_params();