WSDL, aka Web Services Description Language, is a xml format created in 2000.
The Web Services Description Language (WSDL ) is an XML-based interface definition language that is used for describing the functionality offered by a web service. The acronym is also used for any specific WSDL description of a web service (also referred to as a WSDL file), which provides a machine-readable description of how the service can be called, what parameters it expects, and what data structures it returns. Therefore, its purpose is roughly similar to that of a method signature in a programming language. Read more on Wikipedia...