An
addendum or
waiver on an
ISP's
contract which allows
spammers to operate on that network with the express permission of the
ISP.
Pink contracts allow an ISP to look pious about prohibiting spam with a strict AUP, while they're secretly raking in the big bucks. For this reason, they are particularly unpopular among anti-spam activists.
PSInet and AT&T are among the major ISPs known to have signed a pink contract with spammers.
Update (9 Nov 2000):
PSInet has since canceled the specific pink contract that made them the focus of attention, but has not said whether any others are in force.