Unit
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.
A unit is one of the three groupings the Sudoku rules apply to: a row (nine horizontal cells), a column (nine vertical cells), or a 3×3 box. Every cell on the grid belongs to exactly three units — its row, its column, and its box — and the rule says no digit can repeat within any one of them.
Why the term exists
"Unit" is the abstraction that lets one rule cover three different shapes. Without it, Sudoku rules would have to be stated three times: no digit repeats in a row, no digit repeats in a column, no digit repeats in a box. With it: no digit repeats in a unit. Every technique that applies to rows usually applies symmetrically to columns and boxes — the proof is the same, the unit shape just changes.
Where you'll see the term
Articles and technique entries use the word constantly. "Scan the unit for missing digits." "If a digit's last possible cell within a unit is determined, it goes there." The word covers all three shapes simultaneously, which is shorter and more general than naming each separately.
The perspective shift between scanning cells (looking for naked singles) and scanning units (looking for hidden singles) is one of the foundational mental moves in solving. For a longer take, see From scanning cells to scanning units. For the foundational rules a beginner should know, see How to play Sudoku.
See also
- Candidate— 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.
- Given— 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.
- Naked single— A cell on the Sudoku grid that has only one legal candidate left — the simplest deduction in the game, and the one that solves most of an easy puzzle.
Read more
- How to Play Sudoku: The Complete Beginner's Guide
Learn the rules of Sudoku, the core solving moves, and the habits that take a beginner from confused to confident in a single afternoon.
- From scanning cells to scanning units
The single biggest perspective shift between beginner and intermediate Sudoku — what it looks like, why it matters, and how to make it automatic.