SOAP(Simple Object Access Protocol) is an XML based messaging protocal, REST is an architectural style.

SOAP uses WSDL which is an XML document to describe the interface between services. REST uses get, post, put, delete etc. for interfacing between services.

SOAP is XML based, REST can have any payload but JSON is the most widely used because of its ease of readability and speed of processing compared to XML.

SOAP is a specification, REST only has guidelines.