SOAP in ASP.NET

SOAP - Simple Object Access Protocol.
The webservices or WCF services in Asp.net make use of SOAP protocol to access the contents and execute the required operations

SOAP is a simple and open standard XML-based protocol for exchanging information between computers.

http://www.w3schools.com/soap/default.asp

http://www.tutorialspoint.com/soap/index.htm

http://www.codeproject.com/Articles/38839/Test-Your-ASP-NET-WebService-using-SoapUI

http://www.codeguru.com/csharp/csharp/cs_webservices/tutorials/article.php/c12009/Using-SOAP-Headers-with-ASPNET-20-Web-Services.htm