Go (game)
Two players, "Black" and "White", take turns placing a "stone" (game piece) of their own color on a vacant "point" (intersection) of the grid on a Go board. Black plays first. If there is a large difference in skill between the players, the weaker player typically uses Black and is allowed to place two or more stones on the board to compensate for the difference (see Go handicaps). The official grid comprises 19×19 lines, though the rules can be applied to any grid size. 13×13 and 9×9 boards are popular choices to teach beginners, or for playing quick games. Once placed, a stone may not be moved to a different point.
Rules of Go
In the first diagram below, it is White's turn. White must prevent Black from connecting the marked stones to the others by playing at "a". The second diagram shows White's move. White is threatening to kill the marked black stones by playing at "b". In the third diagram, Black plays at "b" to prevent this, capturing White 1. However, by playing at "a" again, White can capture Black 2's group. This is not barred by the ko rule because the resulting position, shown in the fourth diagram, differs from the one after White 1 by the absence of the marked black stones. This kind of capture is called a "snapback".