A binding is a top level WSDL object that provides a concrete specification regarding the transmission of messages to and from a web service. A binding references exactly one port type. The structure of a binding corresponds very closely to that of the port type. The binding contains extensibility elements (for example, SOAP, HTTP, and MIME) that specify protocol specific details. Each port within a Service references exactly one binding.
You can create a binding by right clicking in any blank area in the design workspace and selecting Add Binding in the contextual menu. You can create a new binding or reuse an existing one.