The puzzle is played on a grid, typically rectangular with no standard size. Some cells of the grid start containing numbers. The goal is to determine whether each of the cells of the grid is "black" or "white".
The black cells form "the nurikabe" : they must all be orthogonally
contiguous (form a single polyomino), number-free, and contain no 2x2 or
larger solid rectangles .
The white cells form "islands" : each number n must be part of
an n-omino composed only of white cells. All white cells must belong to exactly one island; islands must have exactly one numbered cell.
Solvers will typically shade in cells they have deduced to be black and dot (non-numbered) cells deduced to be white.