It is a new game type, created by W'rkncacnter, of which the basic goal is to be the last person standing at the end of a round. If someone dies during a round, he may not play until the round ends, and when it does end, the last person standing gets a point. The person with the most points at the end wins.
It is also comaptible with teams and has a faster-paced, less strategic timed mode. The Readme gives more information on playing.