A server that is configured to detect an intruder by mirroring a real production system. It appears as an ordinary server doing work, but all the data and transactions are phony. Located either in or outside the firewall, the honeypot is used to learn about an intruder's techniques as well as determine vulnerabilities in the real system.
A "honeynet" is a network containing honeypots. A "virtual honeynet" is one that resides in a single server, but pretends to be a full network. See firewall