Rules & terminology

In Killer Sudoku, a contiguous group of cells outlined by a dotted line, with a printed sum the digits inside must add up to. Replaces the classic Sudoku given.

A digit (1–9) a cell could still legally hold — one not yet ruled out by anything in its row, column, or 3×3 box. Every empty cell has between one and nine.

A digit pre-filled into a cell at puzzle start — a clue placed by the puzzle's setter. Givens cannot be changed by the player; the rest of the grid has to be solved around them.

A small handwritten or app-rendered note inside a cell indicating which digits the cell could still legally hold. The visible representation of a cell's candidate set.

Collective name for a row, column, or 3×3 box — the three groupings Sudoku's no-repeats rule applies to. Every cell sits in exactly three: its row, column, and box.