[DI Glossary] DeliveryUunit

The DI glossary defines "Delivery Unit" as

     A set of material transferred between two cooperating web programs
     as the response to a single HTTP request. The transfer might, for
     example, be between an origin server and a user agent.
     Users are not normally aware of individual delivery units.

(<http://www.w3.org/TR/di-gloss/#def-delivery-unit>)

So this cannot mean an (X)HTML document plus the referenced images, 
scripts, style sheets, etc, because they are retrieved by different HTTP 
requests each. So what is a delivery unit then?
-- 
Johannes Koch
In te domine speravi; non confundar in aeternum.
                             (Te Deum, 4th cent.)