A standard means of web-based application to application communication, running on a variety of platforms and/or frameworks, sharing metadata, often publicly available to calling software. WS-Policy describes the capabilities and requirements, WS-Transfer describes the end-point resources, WSDL describes the messaging, WS-Security and WS-Trust describe how to protect the communications, XML schema describes the contents, SOAP (protocol) describes the use of XML and HTTP as a messaging protocol.

Source: http://identityaccessman.blogspot.com/2006/08/identity-dictionary.html