Sudoku has its own vocabulary that can be confusing to newcomers and even intermediate players. Whether you are reading a technique guide, following a puzzle walkthrough, or discussing strategies with other solvers, knowing the correct terminology makes everything clearer. This glossary defines every important Sudoku term alphabetically, with links to detailed guides where available.
How to Use This Glossary
Browse alphabetically or use your browser’s search function (Ctrl+F or Cmd+F) to jump to a specific term. The “Related Concept” column links to relevant technique pages and articles for deeper learning.
Complete Sudoku Glossary
| Term | Definition | Related Concept |
|---|---|---|
| ALS (Almost Locked Set) | A group of N cells in a single house containing N+1 candidates. Used in advanced chain-based techniques. | Advanced chains |
| Arrow | In Arrow Sudoku, a constraint where the digit in a circle equals the sum of digits along the arrow. | Sudoku variants |
| Bivalue Cell | A cell with exactly two candidates remaining. Bivalue cells are critical for techniques like XY-Wing and simple chains. | XY-Wing |
| Block | Another name for a 3×3 box. See “Box.” | Box |
| Box | One of the nine 3×3 sub-grids in a standard Sudoku. Each box must contain digits 1–9 exactly once. Also called block, region, or square. | Sudoku rules |
| Box-Line Reduction | When a candidate within a box is confined to a single row or column, that candidate can be eliminated from that row or column outside the box. Also called pointing. | Box-Line Reduction |
| Brute Force | A solving method that tries digits and backtracks upon contradiction. Not considered logical solving. | Solver guide |
| Cage | In Killer Sudoku, a group of cells with a target sum. Digits cannot repeat within a cage. | Killer Sudoku |
| Candidate | A digit that could potentially be placed in an empty cell based on current constraints. Also called a pencil mark or note. | Pencil marks |
| Cell | A single square in the Sudoku grid. A standard 9×9 grid has 81 cells. | Sudoku rules |
| Chain | A sequence of logical inferences connecting cells through strong and weak links. Chains power advanced techniques like X-Chains, XY-Chains, and Alternating Inference Chains. | Advanced techniques |
| Claiming | When a candidate in a row or column is confined to a single box, that candidate can be eliminated from other cells in that box. | Pointing Pair |
| Clue | See “Given.” | Given |
| Coloring | A technique that assigns two colors to candidates connected by conjugate pairs (strong links) and uses contradictions to eliminate candidates. Also called simple coloring or singles chains. | Advanced techniques |
| Column | A vertical line of nine cells in the grid, labeled 1–9 from left to right. Each column must contain digits 1–9 exactly once. | Sudoku rules |
| Conjugate Pair | Two cells in a house where a particular candidate appears exactly twice. If the candidate is not in one cell, it must be in the other. Also called a strong link for that digit. | Strong Link |
| Constraint | A rule that limits which digits can appear in a cell. Standard Sudoku has three constraint types: row, column, and box. | Sudoku rules |
| Crosshatching | A scanning technique where you mentally draw lines through a box from placed digits in intersecting rows and columns to find where a digit must go. | How to play |
| Diagonal | In X-Sudoku, the two main corner-to-corner diagonals, each of which must contain digits 1–9 exactly once. | Sudoku variants |
| Digit | One of the numbers 1–9 used in standard Sudoku. The digits are symbols — no arithmetic is involved in classic Sudoku. | Sudoku rules |
| Elimination | The process of removing a candidate from a cell because logic proves it cannot be the solution for that cell. | Techniques |
| Fin | An extra candidate cell in a fish pattern that prevents it from being a standard fish. Finned and Sashimi fish are variants of X-Wing and Swordfish. | X-Wing |
| Fish | A family of techniques (X-Wing, Swordfish, Jellyfish) based on candidate patterns across rows and columns. Named for the pattern’s visual resemblance. | X-Wing |
| Given | A digit pre-placed in the grid at the start of the puzzle. Also called a clue. The number of givens affects puzzle difficulty. | Sudoku difficulty |
| Grid | The entire Sudoku puzzle — all 81 cells arranged in 9 rows and 9 columns. | Sudoku rules |
| Hidden Pair | Two candidates that appear in exactly two cells within a house. All other candidates can be removed from those two cells. | Hidden Pair |
| Hidden Single | A candidate that appears only once in a house (row, column, or box). That candidate must be placed in that cell. | Hidden Single |
| Hidden Triple | Three candidates confined to three cells in a house. Other candidates can be removed from those three cells. | Advanced techniques |
| Hidden Quad | Four candidates confined to four cells in a house. Other candidates can be removed from those four cells. | Advanced techniques |
| House | Any complete group of nine cells that must contain digits 1–9 exactly once. There are 27 houses: 9 rows, 9 columns, and 9 boxes. | Sudoku rules |
| Intersection | The overlap between a row or column and a box. Each intersection contains 1–3 cells. | Box-Line Reduction |
| Jellyfish | A fish pattern using four rows and four columns. If a candidate appears in only four columns across four rows, it can be eliminated from those columns in other rows. | Advanced techniques |
| Killer Sudoku | A variant that adds cage constraints with target sums and no-repeat rules within cages. | Killer Sudoku |
| Line | A row or column. “Line” is used when the distinction between row and column does not matter. | Sudoku rules |
| Locked Candidates | When candidates for a digit in a box are confined to a single line (pointing) or candidates in a line are confined to a single box (claiming). | Pointing Pair |
| Mini Sudoku | A smaller Sudoku grid (4×4 or 6×6) using fewer digits. Ideal for beginners and children. | Mini Sudoku |
| Naked Pair | Two cells in a house that contain exactly the same two candidates and nothing else. Those two digits can be eliminated from all other cells in the house. | Naked Pair |
| Naked Single | A cell with only one candidate remaining. The digit is immediately placed. Also called a sole candidate. | Naked Single |
| Naked Triple | Three cells in a house whose combined candidates contain exactly three digits. Those three digits can be eliminated from all other cells in the house. | Advanced techniques |
| Naked Quad | Four cells in a house whose combined candidates contain exactly four digits. Those four digits can be eliminated from all other cells in the house. | Advanced techniques |
| Notation | See “Pencil Marks.” | Pencil marks |
| Pattern | A recognizable arrangement of candidates across cells that enables specific eliminations. Fish, wings, and chains are all pattern types. | Techniques |
| Peer | Any cell that shares a house (row, column, or box) with a given cell. Each cell has 20 peers (8 in its row + 8 in its column + 4 additional in its box). | Sudoku rules |
| Pencil Mark | A small number written in a cell to indicate a possible candidate. Also called a note or candidate mark. | Pencil marks |
| Pincer | In an XY-Wing, the two cells that share a candidate with the pivot and whose common peer cells see eliminations. | XY-Wing |
| Pivot | In an XY-Wing, the central bivalue cell connected to both pincers. | XY-Wing |
| Pointing | When a candidate in a box exists only in one row or column of that box, it can be eliminated from that row or column outside the box. | Pointing Pair |
| Puzzle | A Sudoku grid with some cells pre-filled (givens) that has exactly one valid solution. | Sudoku rules |
| Region | See “Box.” Sometimes used more broadly to mean any constraint group. | Box |
| Row | A horizontal line of nine cells in the grid, labeled 1–9 from top to bottom. Each row must contain digits 1–9 exactly once. | Sudoku rules |
| Scanning | The basic technique of visually checking rows, columns, and boxes for placed digits to find cells where a digit must or cannot go. | How to play |
| Singleton | A cell with only one candidate. See “Naked Single.” | Naked Single |
| Snyder Notation | A pencil-marking method that only notes a candidate when it appears in exactly two cells within a box. Named after World Sudoku Champion Thomas Snyder. | Pencil marks |
| Solved Cell | A cell whose digit has been determined, either as a given or through logical deduction. | — |
| Strong Link | A connection between two cells for a specific digit where exactly two positions exist in a house. If the digit is not in one cell, it must be in the other. | Coloring, Chains |
| Subset | A group of N candidates confined to N cells within a house (naked subset) or N cells containing only N candidates (hidden subset). | Naked Pair, Hidden Pair |
| Sudoku | A logic puzzle played on a 9×9 grid divided into nine 3×3 boxes. The objective is to place digits 1–9 such that each row, column, and box contains each digit exactly once. | How to play |
| Swordfish | A fish pattern using three rows and three columns. If a candidate appears in only three columns across three rows, it can be eliminated from those columns in other rows. | Advanced techniques |
| Thermometer | In Thermometer Sudoku, a shape on the grid requiring digits to increase from bulb to tip. | Sudoku variants |
| Trivalue Cell | A cell with exactly three candidates remaining. Important for XYZ-Wing patterns. | XYZ-Wing |
| Unique Solution | A puzzle has a unique solution if there is exactly one valid way to complete the grid. All properly constructed Sudoku puzzles have a unique solution. | Sudoku rules |
| Unit | See “House.” The terms are interchangeable. | House |
| Weak Link | A connection between two cells for a specific digit where if the digit is in one cell, it cannot be in the other — but the digit being absent from one cell does not guarantee it is in the other. | Chains |
| Wing | A family of techniques (XY-Wing, XYZ-Wing, W-Wing) that use bivalue and trivalue cells to make eliminations through shared peers. | XY-Wing, XYZ-Wing |
| X-Wing | A fish pattern using two rows and two columns. If a candidate appears in only two columns across two rows, it can be eliminated from those columns in other rows. | X-Wing |
| XY-Wing | A technique using three bivalue cells: a pivot connected to two pincers. Any cell that sees both pincers can have the shared candidate eliminated. | XY-Wing |
| XYZ-Wing | Similar to XY-Wing but the pivot is a trivalue cell. Eliminations occur in cells that see all three wing cells. | XYZ-Wing |
Terms by Category
If you prefer to browse by topic rather than alphabetically, here are the most important terms grouped by category:
Grid Structure
Cell, Row, Column, Box (Block, Region), House (Unit), Grid, Peer, Line, Intersection, Diagonal
Puzzle Elements
Digit, Given (Clue), Candidate (Pencil Mark, Note), Solved Cell, Unique Solution, Constraint, Puzzle
Basic Techniques
Scanning, Crosshatching, Naked Single (Singleton), Hidden Single, Elimination
Intermediate Techniques
Naked Pair, Hidden Pair, Naked Triple, Hidden Triple, Locked Candidates (Pointing, Claiming, Box-Line Reduction), Subset
Advanced Techniques
X-Wing, Swordfish, Jellyfish, Fish, Fin, XY-Wing, XYZ-Wing, Wing, Pincer, Pivot, Chain, Strong Link, Weak Link, Conjugate Pair, Coloring, ALS, Brute Force
Notation Systems
Pencil Mark, Snyder Notation, Full Notation, Notation, Bivalue Cell, Trivalue Cell
Variants and Special Terms
Killer Sudoku, Cage, Mini Sudoku, Arrow, Thermometer, Diagonal
Building Your Vocabulary
You do not need to memorize every term at once. Start with the fundamentals:
- Learn the grid terms first — cell, row, column, box, house, digit, given, candidate. These appear in every guide and tutorial.
- Add technique names as you learn them — Naked Single, Hidden Single, Naked Pair, and Pointing Pair cover most intermediate solving.
- Pick up advanced vocabulary naturally — terms like conjugate pair, strong link, and ALS will make sense once you study the techniques that use them.
For a structured learning path, start with our guide on how to play Sudoku, then explore beginner strategies and advanced strategies. Each guide uses the terminology defined here and links back to this glossary when introducing new terms.
Frequently Asked Questions
What is a house in Sudoku?
A house is any complete group of nine cells that must contain the digits 1–9 exactly once. In standard 9×9 Sudoku, there are 27 houses: 9 rows, 9 columns, and 9 boxes. The term exists because saying “row, column, or box” repeatedly is cumbersome. You may also see the synonym “unit.”
What is the difference between a candidate and a given?
A given (also called a clue) is a digit pre-placed in the puzzle at the start — it is fixed and cannot be changed. A candidate is a possible digit for an empty cell that has not yet been eliminated by logic. As you solve, candidates are removed through elimination until each empty cell has only one candidate remaining.
What does elimination mean in Sudoku?
Elimination is the core solving action in Sudoku. It means removing a candidate from a cell because logical deduction proves that digit cannot be the answer for that cell. The simplest elimination: when a digit is placed in a row, it is eliminated as a candidate from every other cell in that row (and its column and box). Advanced techniques perform more complex eliminations across multiple cells and houses.
What is the difference between a strong link and a weak link?
A strong link exists between two cells for a digit when those are the only two cells in a house that contain that candidate. If the digit is not in one cell, it must be in the other. A weak link means if the digit is in one cell, it is not in the other — but the reverse is not guaranteed. Both link types are used in chain-based advanced techniques.
Do I need to know all these terms to solve Sudoku?
No. You can solve easy and many medium puzzles knowing only the basic terms: cell, row, column, box, and candidate. More precise vocabulary becomes useful as you tackle hard and evil puzzles and study advanced techniques. Think of this glossary as a reference you return to as needed, not a list to memorize.