Web Single Sign-On Metadata Exchange Protocol
Web Single Sign-On Metadata Exchange Protocol is a Web Services and Federated identity specification, published by Microsoft and Sun Microsystems that defines mechanisms for a service to query an identity provider for metadata concerning the protocol suites it supports. The goal of this operation is to increase the ability of a given service to interoperate with a given identity provider.
Source: Wikipedia — Web Single Sign-On Metadata Exchange Protocol (CC BY-SA 4.0)