from the design for humans acting like humans file:

"What is contingency design?
Things go wrong online. Contingency design is the way the creators of the site right the ship. It includes error messaging, instructive text, information architecture, programming, and graphic design. Successful contingency design helps wayward surfers succeed at their goals in obtaining information, completing a transaction, or other tasks. Poor contingency design results in frustration and lost visitors. "

Visit design not found for examples.

Thanks, Marc, for reminding me of this site!