Its a general statement to explain that the response object itself is not sent to the client, instead it is converted to an actual HTTP response which will just contain headers and body of the response...
1. A single status code
A status code is an integer value that describes the status of the response. The status code can indicate success or failure.
2. HTTP headers
Response headers that tell the client things like what software the server is running and the content type of the server's response
3. Response body
The response body is the main content of the response. For an HTML page, the response body is the HTML itself. For a graphic, the response body contains the bytes that make up the image. A response body can be of any type and of any length.