What is the origin of the expression 'zero-sum game' and what does it mean?

A zero-sum game is one in which no wealth is created or destroyed. So, in a two-player zero-sum game, whatever one player wins, the other loses. Therefore, the player share no common interests. There are two general types of zero-sum games: those with perfect information and those without.

In a game with perfect information, every player knows the results of all previous moves. Such games include chess, tic-tac-toe, and Nim. In games of perfect information, there is at least one "best" way to play for each player. This best strategy does not necessarily allow him to win but will minimize his losses. For instance, in tic-tac-toe, there is a strategy that will allow you to never lose, but there is no strategy that will allow you to always win. Even though there is an optimal strategy, it is not always possible for players to find it. For instance, chess is a zero-sum game with perfect information, but the number of possible strategies is so large that it is not possible for our computers to determine the best strategy.

In games with imperfect information, the players do not know all of the previous moves. Often, this occurs because the players play simultaneously. Here are some examples of such games:

Rock, Paper, Scissors

Zero-sum Game Origin
"We shall call games of the first-mentioned type zero-sum games, and those of the latter type non-zero-sum games." --Theory of Games and Economic Behavior, John Von Neumann & Oskar Morgenstern, 1944.

The creation of the zero-sum game concept and it's first mention in text comes from Theory of Games and Economic Behavior. Written by the mathematician John Von Neumann and the economist Oskar Morgenstern. The book is credited with creating the mathematical field of game theory. With zero-sum games being a crucial part of that field.