Code for a nice set of boobs.
The etymology (ooooh, I know big words :-D) of this word starts with the need to avoid the use of the word 'Rack' (so as to alert a friend to a lovely set of bazookas WITHOUT the target being alerted). Thus (-> = becomes):-
Rack -> Tray (Vague) -> Milk Tray (Breasts) -> Cadburys' (as in 'All because the lady HAS....).
That's a nice set of Cadburys'...