British slang describing a girl of loose morals (a slut) who has been with a few too many guys. Normally a very nice girl to talk to but also a bit thick. Also has no problem being passed around a group of mates.
Comes from a box of Roses being a box of assorted creams.
Ian - I'd shag that Lisa any time, she's well fit.
Me - Aye, I've heard she's a proper Cadbury's Fanny though.