The total file size sent from the web server to the end
user. This does not include HTTP headers in served objects,
HTTP request headers from users, nor bytes needed by the
underlying network protocols
HTTP Header
Every HTTP transaction with a server sends a header with
it. Click for a
list of HTTP headers
Referring URL
The URL, from the web page perspective, that points to
it. You can tell who is visiting your web page by looking at
the referring URL which is contained in the HTTP header.