Komi and the half point

Black plays first, and in an even game the first move is worth something: a few points of board, on average. So White is given a fixed number of points at the end, called komi, to make up for moving second.

Komi began small in mid-twentieth-century Japanese tournaments and was raised as players learned how much the first move was really worth. Today professionals in Japan and Korea use 6.5 points; Chinese rules and the American Go Association use 7.5. The Go page here uses 7.5.

The half point is deliberate. Stones and territory always count in whole numbers, so adding half a point means a game can never end in a tie: one side always wins, even if by the smallest possible margin.