SOAP (formerly known as Simple Object Access Protocol) is a lightweight protocol for exchanging structured and typed information in a decentralized, distributed environment. It is an XML-based protocol that consists of three parts:

An envelope that defines a framework for describing what is in a message and how to process it.
A set of encoding rules for expressing instances of application-defined data types.
A convention for representing remote procedure calls and responses.
SOAP makes possible a universal platform for Web-based applications that transcend the boundaries of a specific programming language and/or specific platform. With SOAP users/adaptors growing by the day, SOAP is rapidly becoming the standard for building Web services and connecting disparate systems in a loosely coupled fashion with complete platform independence.

SOAP was developed by Microsoft, DevelopMentor, and Userland Software and proposed as an XML protocol to the World Wide Web Consortium (W3C). The name reflected the idea that SOAP would be used to express serialized object graphs, enabling object-oriented systems to perform functions such as remote procedure calls while preserving objects and their relations. However, in the W3C's latest working draft (version 1.2), SOAP became the name and is no longer an acronym. This reflects a shift in thinking about SOAP from a serialization framework for object-oriented systems to a more general XML-based messaging paradigm, where the messages do not necessarily contain objects.