SOAP

From https://en.wikipedia.org/wiki/SOAP:  SOAP (formerly a backronym for Simple Object Access Protocol) is a messaging protocol specification for exchanging structured information in the implementation of web services in computer networks. It uses XML Information Set for its message format, and relies on application layer protocols, most often Hypertext Transfer Protocol (HTTP), although some legacy systems communicate over Simple Mail Transfer Protocol (SMTP), for message negotiation and transmission. SOAP allows developers to invoke processes running on different operating systems (such as Windows, macOS, and Linux) to authenticate, authorize, and communicate using Extensible Markup Language (XML). Since Web protocols like HTTP are installed and running on practically all operating systems, SOAP allows clients to invoke web services and receive responses independent of language and platforms

See also https://www.w3.org/TR/soap/