What is "nurikabe"

n. (context games puzzles English) A Japanese logic puzzle with a rectangular grid of squares, some of them numbered; the solver is challenged to fill in a subset of squares (under certain constraints) such that each numbered square finally indicates the number of unfilled squares contiguous to it.

Nurikabe ( hiragana: ぬりかべ) is a binary determination puzzle named for Nurikabe, an invisible wall in Japanese folklore that blocks roads and delays foot travel. Nurikabe was apparently invented and named by Nikoli; other names (and attempts at localization) for the puzzle include Cell Structure and Islands in the Stream.

The nurikabe (ぬりかべ) is a Yōkai, or spirit, from Japanese folklore. It manifests as a wall that impedes or misdirects walking travelers at night. Trying to go around is futile as it extends itself forever. Knocking on the lower left part of the wall makes it disappear. It has been suggested that the legend was created to explain travellers losing their bearings on long journeys.