Web services – user sends request to server , gets response back . Two types of commonly used protocols are soap and rest.

Soap is xml based and all rules are defined in wsdl document. wsdl is web service descriptor language. In Soap request and response are in the form on xml .

Rest –based in Json. Most of apis present today are based on rest. All request and response are in the form of json.

One big difference between Rest and Soap is soap is a protocol , while rest is an architecture. That is why rest is more popular than rest.