noun
open skirt; open edge territory
In go, a shape where the edge territory is not fully closed, leaving a gap that the opponent can invade. The term likens the open edge to the hem of a skirt.
この形はスソアキがあるので、相手に打ち込まれやすい。
This shape has an open skirt, so it's easy for the opponent to invade.
スソアキを放置すると、そこから荒らされる。
If you leave an open skirt unattended, your territory will be wrecked from there.
Compound of 裾 (すそ, 'hem, skirt') and 空き (あき, 'opening, gap'). The term is specific to go and describes a territorial weakness along the edge.