Shade some cells so that all remaining cells are connected orthogonally and no two black cells share an edge. Each numbered cell indicates the total count of unshaded cells connected in line vertically and horizontally to the numberer cell including the cell itself.
(Rules and example from PGP IB)
History of the puzzle
First appeared on Nikoli volume 34 (1991). Invented by "Tea.M". Original name 黒マスはどこだ "Kuromasu wa doko da" means "where is black cell?" In Nikoli, the name was later contracted to 黒どこ "Kurodoko". Kuromasu, the first word of the name, means "black cell".