I see a web services terminology called Payload and what exactly is it ?
As i understood Payload is nothing but the message which is commonly found to be in XML form.
This following link will give you a better picture of the usage.
Payload is something one carries. A paperboy's payload is a pile of newspapers and a HTTP POST request's payload is whatever comes in the "body". HTTP GET doesn't have payload because it doesn't have a "body" (although custom HTTP headers and request parameters could be considered as payload).