SOAP: Simple Object Access Protocol. Dynamically generated HTML content works fine in Web browsers, but it presents a nightmare for anyone trying to utilize that data with other programs. For example, you can easily view an auction site in a browser, but an application would require a complex HTML parser to read your bid's status from the same site. Worse, you would need a different parser to track a different auction site, and the simplest redesign of either site could throw off your program.
Web services solve this problem with a consistent and easy method for accessing online information. Web services could potentially create a whole new type of Web.
A protocol created by Microsoft, DevelopMentor, and Userland Software and backed by companies that include IBM, Lotus, and Compaq gives a big push toward that vision. Simple Object Access Protocol (SOAP) exchanges application data over HTTP in XML encoding.
The above article on CNET covers SOAP using Perl. Get the PHP implementation of SOAP.