It is a small school joke.
In this game the chess game is played, and the names of cities on the certain letter are made. It reminds a lesson of geography.
All rules as in orthodox chess with the following changes:
For example. The player wants to move Rook. He speaks: "Rotterdam". And only then moves Rook.
It becomes amusing, when can not recollect the name of city, and the situation in game requires movement of such piece. Whether there are a lot of names of cities you remember, for example, on the letter "P" (for pawn's movement).