Response is a read-only TIdHTTPResponse property that represents the HTTP client connection and connection flags, the numeric reponse code and text, and the content stream used by the HTTP protocol handler. 

The Response property is used in GetResponseHeaders, and allows the protocol handler to provide the values received in a HTTP response. 

Values in the Response property are updated using the RetrieveHeaders method when connecting to the HTTP host and when the request is executed for the HTTP client.

TIdHTTPResponse