A game played by correspondance between players. Two-player games are played by the exchange of mail between the two participants.

In the late 1980s, after the rise of PCs but before the rise of the internet, there was another variation that was more like a multiplayer role-playing game. Participants would mail in their instructions to a central office, and the gamemasters would input the instructions into a PC, then mail back a printout of the results. Ususally one set of moves made in this way would take one week.

The internet soon made these kinds of games obsolete, as they were both slower and more expensive to play in this way; most games cost on the order of 50 cents per turn plus postage.

I believe that chess is still played by mail, however.