Request is a TIdHTTPRequest property used to specify the header values to send to the HTTP server. Request headers allow the HTTP client to pass additional information about the request, or the request client, to the HTTP server. 

Request may contain the textual representation of Cookie values from the HTTP client, Host and Port information for a proxied connection, as well as values from TIdHTTP properties transmitted as message headers. 

Request is used in the protected method that performs the HTTP transfer. 

Use Response to examine header values received in an HTTP protocol response from the server.

TIdCustomHTTP.Response 

TIdCustomHTTP.DoRequest 

TIdHTTPRequest 

TIdHTTPResponse