XRDS (eXtensible Resource Descriptor Sequence) is an XML format for discovery of metadata about a web resource – in particular discovery of services associated with the resource, a process known as service discovery. For example, a website offering OpenID login can resolve a user's OpenID identifier to an XRDS document to discover the location of the user's OpenID service provider.
Read more about XRDS: Background, XRDS Simple, Example Uses, Example XRDS Document, Synonyms, Service Endpoints (SEPs), Service Types, Licensing