What is a WSDL?

The Web Services Description Language (WSDL, pronounced 'wiz-dull' or spelled out, 'W-S-D-L') is an XML-based language that provides a model for describing Web services. Version 1.1 has not been endorsed by the World Wide Web Consortium (W3C). Version 2.0, for which several drafts have been released, is expected to become a W3C recommendation.

WSDL is an XML-based service description on how to communicate using web services. The WSDL defines services as collections of network endpoints, or ports. WSDL specification provides an XML format for documents for this purpose.

The abstract definition of ports and messages is separated from their concrete use or instance, allowing the reuse of these definitions. A port is defined by associating a network address with a reusable binding, and a collection of ports define a service. Messages are abstract descriptions of the data being exchanged, and port types are abstract collections of supported operations. The concrete protocol and data format specifications for a particular port type constitutes a reusable binding, where the messages and operations are then bound to a concrete network protocol and message format. In this way, WSDL describes the public interface to the web service.

WSDL is often used in combination with SOAP and XML Schema to provide web services over the Internet. A client program connecting to a web service can read the WSDL to determine what functions are available on the server. Any special datatypes used are embedded in the WSDL file in the form of XML Schema. The client can then use SOAP to actually call one of the functions listed in the WSDL.

This definition is from The Wikipedia which is published under the GNU Free Documentation License.