soap stands for simple object acess protocol. it is another protocol that works in conjuction with HTTP to call a remote method over different platform and technology. it is xml based protocol and platform-agnostic. the same thing i.e call to remote method can be had by JRMP but it requires that the other application too uses the java tech (otherwise problems due to proxyserver and firewalls as they will block the content of other lang). hence we use SOAP.

industrial usage is e.g an industry wants to order TNT as its raw material. it also includes finding the best route to transport and best cost price. so it transfers a request to other services using SOAP requesting for best prices and to other service requesting for the best route. this is the simplest example but soap usually comes into play only when diffrent applications have to communicate with each other.