SOAP (formerly an acronym of Simple Object Access Protocol) is a light-weight protocol for exchanging messages between computer software, typically in the form of software components. The word object implies that the use should adhere the object-oriented programming programming paradigm.
SOAP is an extensible and decentralized framework that can work over multiple computer network protocol stacks. Remote procedure calls can be modeled as an interaction of several SOAP messages. SOAP is one of the enabling protocols for Web services.
SOAP can be run on top of all the Internet Protocols, but HTTP is the most common and the only one standardized by the W3C. SOAP is based on XML, and its design follows the "Head-Body" Pattern, not unlike HTML. The head contains meta-information like information for routing, security and transactions. The body transports the main information.