The Web Services Description Language (WSDL) is an XML-based language used to describe the services businesses offer and to provide a way for individuals and other businesses to access those services electronically.
WSDL is a specification defining how to describe web services in a common XML grammar. WSDL describes four critical pieces of data:

• Interface information describing all publicly available functions
• Data type information for all message requests and message responses
• Binding information about the transport protocol to be used
• Address information for locating the specified service