Sudoku & Kakuro Glossary
Plain-language definitions of the terms used across the guides and the play surfaces.
- Sudoku
- A logic puzzle played on a 9×9 grid: fill every row, column, and 3×3 box so each contains the digits 1 to 9 exactly once. A valid Sudoku has a single solution reachable by logic alone.
- Kakuro
- A number crossword: fill runs of white cells with digits 1 to 9 so each run adds up to its clue, never repeating a digit within a run. Also called cross sums.
- Given
- A digit printed in the puzzle at the start. Givens are fixed clues and cannot be changed.
- Candidate
- A digit that could still legally be placed in a cell. Solving is largely the work of narrowing each cell down to a single candidate.
- Pencil mark
- A small note recording the candidate digits still possible in a cell. Pencil marks make techniques like naked and hidden singles visible.
- Unit
- Any row, column, or box that must contain each digit exactly once. Most Sudoku logic reasons about a single unit.
- Naked single
- A cell with only one remaining candidate, so that digit must go there — the first technique most solvers learn.
- Hidden single
- A digit that can legally go in only one cell of a unit, even when that cell still shows several candidates. The mirror of a naked single.
- Pointing pair
- When the only cells for a digit in a box share one row or column, the digit can be removed from the rest of that line outside the box.
- Box/line reduction
- When the only cells for a digit in a row or column all fall inside one box, the digit can be removed from the rest of that box.
- Naked pair
- Two cells in a unit that share the same two candidates. Those two digits can then be removed from every other cell in the unit.
- X-wing
- An advanced pattern: a digit confined to the same two columns across two rows (or vice versa) allows eliminations elsewhere in those columns.
- Run
- In Kakuro, an unbroken line of white cells, across or down, that must add up to a single clue using distinct digits.
- Clue
- In Kakuro, the target sum for a run, shown in a shaded cell — above the diagonal for the run going right, below it for the run going down.
- Combination
- The set of distinct digits that can fill a Kakuro run of a given length and sum. Many clue-and-length pairs have only one combination.