Understanding Sudoku terminology helps you learn new techniques from books, videos, and online communities. Here's a comprehensive glossary of terms every Sudoku player should know.
Cell: A single square in the Sudoku grid. A standard 9x9 puzzle has 81 cells.
Row: A horizontal line of 9 cells across the grid. There are 9 rows, typically numbered 1-9 from top to bottom.
Column: A vertical line of 9 cells down the grid. There are 9 columns, typically labeled A-I or 1-9 from left to right.
Box (also: Block, Region, Square): One of the nine 3x3 sections outlined by thicker borders. Each box must contain the numbers 1-9.
Unit: Any row, column, or box - the three types of groups where numbers cannot repeat.
Given (also: Clue): A number that is pre-filled when the puzzle starts. These are the starting numbers you work from.
Grid: The entire 9x9 Sudoku puzzle layout.
Band: A horizontal group of three boxes (rows 1-3, rows 4-6, or rows 7-9).
Stack: A vertical group of three boxes (columns 1-3, columns 4-6, or columns 7-9).
Candidate (also: Possibility, Pencil Mark): A number that could potentially go in a cell. Cells with multiple candidates haven't been solved yet.
Pencil Mark (also: Note): Small numbers written in a cell to track candidates. Called "pencil marks" because they're written lightly and erased as candidates are eliminated.
Elimination: The process of removing a candidate from a cell because it's proven impossible.
Naked Single: A cell with only one remaining candidate. The easiest type of placement.
Hidden Single: A candidate that appears in only one cell within a unit, even though that cell has multiple candidates.
Pair: Two cells in the same unit that share exactly the same two candidates.
Naked Pair: Two cells with exactly the same two candidates - those numbers can be eliminated from other cells in the unit.
Hidden Pair: Two candidates that appear in only two cells within a unit - other candidates can be eliminated from those cells.
Triple: Three cells sharing three candidates. Works like pairs but with three numbers.
Quad: Four cells sharing four candidates.
Pointing Pair: When candidates for a number within a box are confined to a single row or column.
Box/Line Reduction (also: Claiming): When candidates for a number in a row or column are confined to a single box.
Cross-Hatching: A scanning technique where you trace a number's occurrences across rows and columns to find where it must go in a box.
Locked Candidates: A general term for candidates that are confined to a specific intersection of units (includes pointing pairs and box/line reduction).
X-Wing: A pattern where a candidate appears in exactly two cells in each of two rows, forming a rectangle. The candidate can be eliminated from the columns.
Swordfish: An extension of X-Wing using three rows and three columns.
Jellyfish: An extension using four rows and four columns.
XY-Wing: Three bi-value cells where a pivot cell shares one candidate with each of two wing cells.
XYZ-Wing: Similar to XY-Wing but the pivot has three candidates.
Coloring (also: Simple Coloring): A technique where candidates are marked in two colors to represent two possible states. Contradictions in one color prove the other must be correct.
Chain: A sequence of linked cells where each link represents a logical implication. Chains can prove that certain candidates must be eliminated.
Forcing Chain: A chain that starts from a cell and follows the logical consequences of placing each candidate.
Remote Pair: A chain of bi-value cells with the same two candidates, connected through units.
Minimal Puzzle: A puzzle where removing any given would make the puzzle have multiple solutions.
Proper Puzzle: A puzzle with exactly one unique solution.
Symmetric Puzzle: A puzzle where the pattern of givens is rotationally symmetric (180 degrees or 90 degrees).
Well-Posed: A puzzle that can be solved through logic alone without guessing.
Difficulty Rating: An assessment of how hard a puzzle is, based on the techniques required to solve it.
Killer Sudoku: A variant using cage sums instead of given numbers.
Cage: In Killer Sudoku, a group of cells with a target sum.
Samurai Sudoku: Five overlapping standard Sudoku grids.
Jigsaw Sudoku: Irregular-shaped regions replace the standard 3x3 boxes.
X-Sudoku: Main diagonals must also contain 1-9.
Thermo Sudoku: Numbers increase along thermometer shapes.
Sandwich Sudoku: Clues indicate the sum between 1 and 9 in each row/column.
World Sudoku Championship: The annual international Sudoku solving competition organized by the World Puzzle Federation.
Time Penalty: Points deducted for errors in competitive solving.
Puzzle Point Value: Points awarded for completing a puzzle in competition, based on difficulty.
This glossary covers the most commonly used Sudoku terms. As you advance in skill, these terms become second nature and help you communicate with the broader Sudoku community.
A naked single is a cell that has only one remaining candidate after all eliminations from its row, column, and box. It is the simplest and most fundamental solving technique - when a cell can only contain one possible number, that number must go there.
A naked pair consists of two cells in the same unit that contain exactly the same two candidates and no others. A hidden pair consists of two candidates that appear in only two cells within a unit, but those cells may contain other candidates as well. In a naked pair, you eliminate the pair's numbers from other cells. In a hidden pair, you eliminate the other candidates from the pair's cells.
A unit refers to any row, column, or box in the Sudoku grid - the three types of groups where the numbers 1-9 must each appear exactly once. Every cell belongs to exactly three units: one row, one column, and one box.
Cross-hatching is a scanning technique where you trace where a specific number already appears in rows and columns to determine where that number must go in a particular box. By eliminating rows and columns that already contain the number, you can often narrow down its position to a single cell.
An X-Wing occurs when a candidate number appears in exactly two cells in each of two different rows, and those cells line up in the same two columns (forming a rectangle). When this pattern is found, the candidate can be eliminated from all other cells in those two columns, because the number must occupy one diagonal pair of the rectangle.
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