1. A box designed to attract crackers so that they can be observed in action. It is usually well isolated from the rest of the network, but has extensive logging (usually network layer, on a different machine). Different from an iron box in that its purpose is to attract, not merely observe. Sometimes, it is also a defensive network security tactic — you set up an easy-to-crack box so that your real servers don't get messed with. The concept was presented in Cheswick & Bellovin's book Firewalls and Internet Security.
2. A mail server that acts as an open relay when a single message is attempted to send through it, but discards or diverts for examination messages that are detected to be part of a spam run.