Go is a abstract strategy game of ancient origins. The tokens have roughly the shape of ellipsoids of revolution and are called “stones”. The board consists of a grid, which has as many intersections horizontally as vertically. Boards with 9, 13 or 19 intersections per side are typical. The game is for 2 players, called “black” and “white” which have an unlimited supply of stones of their color. Players alternate turns placing their stones in empty intersections and afterwards removing the continuous groups of stones of the opposite color than have no adjacent empty intersections or passing. Players may pass at any time, but it's only prudent to do so when there are no more useful moves. The game ends when both players pass consecutively and they agree on which stones are dead (Would be eventually captured), the player with the greatest score wins. Score depends on the komi (compensation for white, for playing second), the number of stones he has on the board, and the empty intersections completely surrounded by his stones.
The exact rules are slightly more complex as it's need to specify ways to avoid reverting to a previous position in a loop, the procedure to mark dead stones as captured at the end of the game, and the method by which score is computed. Among the simplest and most elegant rules are the Tromp-Taylor rules, the American Go Association rules and the British Go Association rules (See BGA Rules, Concise AGA Rules, Complete AGA Rules. The BGA rules are equivalent to the AGA rules except for the treatment of illegal moves).