Zen-Go is a game played by more than two and an odd number of players, that alternately play Black and White stones. That means, that after every full rotation you will play with the other color.
 
On Dragon the notation "Zen-Go (5)" represents a Zen-Go game played by 5 players.
 
This game type can be a lot of fun and can teach you to look on the whole board situation instead of relying on "hidden" tactics, because in the next rotation colors are switched and you have to make a move to counter your own tactics.
 
If a stronger player participates you may ask him to add a review of the game, which could make such a game into a good learning experience.
 
For more information on Zen-Go, see: http://senseis.xmp.net/?ZenGo