In Go, tizi (提子) is a term that refers to the act of capturing an opponent's dead stone.
A stone is considered to be dead if it has no qi, which is the life force of a stone. Qi is calculated by counting the number of empty intersections that are directly connected to a stone. A stone with four qi is alive, a stone with three qi is alive but may be captured, and a stone with two qi or fewer is dead.
When a stone has no qi, it is considered to be dead and can be captured by the opponent. This is done by placing a stone on the intersection that is the only connection to the dead stone. The dead stone is then removed from the board.
Tizi is an important concept in Go. It is essential for understanding how to capture your opponent's stones and how to protect your own stones from being captured.