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Susoaki

A shape defect in which the lower edge of a group is left open, creating a possible back-door weakness.

Also known as

Open skirt

Susoaki—also known as Open skirt—describes a group whose lower edge or side has an opening. That gap may provide the opponent with a route for an invasion, reduction, forcing move, or attack, depending on the surrounding stones and the group’s liberties.

The term identifies a structural weakness to consider when judging a group’s safety and stability. It describes a shape condition, not a particular move, so its importance is determined by the local position. An open edge is not automatically exploitable: the surrounding stones, available liberties, and results of careful tactical reading must all be evaluated.