CCP announced in a dev blog entry today that EVE Online is about to get a second test server called, appropriately enough, Duality. So why does the game need two test servers? Test Lead CCP Hypnotic explains:

"The product of an internal QA naming contest, Duality, already being nicknamed 'Ducie,' will be our brand new public facing Event Server. This is in contrast to Singularity, which is a Public Server. The difference is that where Singularity is up and running and open to players almost 24/7, Duality will only be opened for special CCP run events. You're already familiar with these events because we've been running them on Singularity up until now. Things like the weekly mass tests, or guided play tests will, in the future, happen on Duality with much better coordination and preparation than what was capable on Singularity in the past. These events are vitally important to the quality of EVE Online."

More information about Duality can be found on the EVElopedia page.