WSDL
Web Services Description Language is an XML-based, platform-independent meta language, which is used to describe the interface definitions of a Web service.
WSDL mainly defines the functions of the Web service that are externally accessible, as well as the parameters and return values of these operations. Furthermore, it describes the communication format in which function calls are sent to Web services. The URL at which a Web service can be called is also specified.
A Web service must be published before the WSDL document describing it can be found, imported, and used. The publication contains detailed information on the location where the descriptive WSDL document was found.
Specifically, a WSDL document contains functional details about:
all information required to access the Web service in machine-readable format.