Applications: service description, registration and discovery, execution.
WSDL is Web Services Description Language. XML format for describing network services. Works with SOAP, HTTP and MIME (email).
DISCO is Discovery of Web Services. Way to discover and retrieve WSDL description of services on remote machines. Using the Discovery Document Format (also an XML grammar), can send a discovery document to a remote server and, if any SOAP enabled services (AKA web service) exist, receive back an WSDL description of the services provided. Crops up in .NET quite a bit.
UDDI is Universal Description, Discovery and Integration. Industry initiative to enable businesses to quickly, easily, and dynamically find and transact with one another. UDDI enables a business to (i) describe its business and its services, (ii) discover other businesses that offer desired services, and (iii) integrate with these other businesses.
XML-RPC is remote procedure calling using HTTP as the transport and XML as the encoding.
SOAP is Simple Object Access Protocol. Lightweight protocol for exchange of information in a decentralized, distributed environment.
ebXML is electronic Business using eXtensible Markup Language. Standard method to exchange business messages, conduct trading relationships, communicate data in common terms and define and register business processes.