The board game Go (played with black and white stones on a grid), also called igo or weiqi.
祖父は毎晩、碁を打っている。
My grandfather plays Go every night.
囲碁のルールでは、石を囲んで陣地を取ることが目的だ。
In Go, the aim is to surround territory by surrounding stones.
彼は碁がとても強く、プロに近い腕前だ。
He is very strong at Go, almost at a professional level.