what is the parameter of webservicecallout.invoke method in Salesforce?

WebServiceCallout.invoke(
Class servicePort, //Usually set to "this", contains httpheader info as well as ?
request_x, //Request object, defining schema, properties, and field order
response_map_x, //Response object, defining schema, properties, and field order
new String[]{
String endpoint, //Endpoint of the service
String ?, //what is this?
String methodSchema, //Schema for the request object?
String method, //Name of the request method?
String responseSchema, //Schema for the response object?
String response, //Name of the response object?
String responseClass} //Name of the Apex class the response will be converted to
);