Web Services Description Language (WSDL): An Intuitive View

Software is continuing to evolve, from the traditional locally hosted applications operating in a closed environment to web services. The web services computing model revolutionizes technology by allowing remotely located individuals to harness information assets and invoke services from virtually anywhere. In order to utilize this technology, one needs to know information about the service provider, such as the protocol of communication, network address, encoding schemes, and method details. Web Services Description Language (WSDL) provides this capability by using XML to communicate this information. WSDL is defined as "an XML grammar for describing network services as collections of communication endpoints capable of exchanging messages."

http://java.sun.com/dev/evangcentral/totallytech/wsdl.html