What is "ponnuki"

is a Japanese term in the game of Go that refers to capturing a single stone, resulting in a diamond shape. The shape of the remaining capturing stones is considered to be very strong, due to its influence in all directions. A certain Go proverb says "A Ponnuki is worth 30 points".

Ponnuki move by Black 1

A diamond shape (4 stones touching the same empty spot) is considered a ponnuki only when constructed by capturing the middle stone.

Depending on the context (other stones on the board), a ponnuki may be strong and thick but inefficient (overconcentrated).