Sudoku Terminology
A complete glossary of Sudoku terms and jargon. Whether you are reading a solving guide or discussing strategies with other players, this reference covers every term you are likely to encounter, from basic grid anatomy to advanced chain logic.
Grid Anatomy
The physical structure of a Sudoku puzzle. Understanding these terms helps you communicate about specific locations and regions in the grid.
Cell
The smallest unit of the Sudoku grid. A standard 9x9 puzzle contains 81 cells arranged in 9 rows and 9 columns. Each cell holds exactly one digit from 1 to 9 in the completed puzzle.
Row
A horizontal line of 9 cells spanning the full width of the grid. There are 9 rows in a standard Sudoku, and each row must contain the digits 1 through 9 exactly once.
Column
A vertical line of 9 cells spanning the full height of the grid. There are 9 columns in a standard Sudoku, and each column must contain the digits 1 through 9 exactly once.
Box / Block / Region
One of the nine 3x3 sub-grids outlined by thicker borders. Each box must contain the digits 1 through 9 exactly once. The terms box, block, and region are used interchangeably across different Sudoku resources.
Unit
A general term for any group of 9 cells that must contain each digit exactly once. In standard Sudoku, there are 27 units: 9 rows, 9 columns, and 9 boxes.
Grid
The entire 9x9 playing field consisting of 81 cells, 9 rows, 9 columns, and 9 boxes. The grid is the complete puzzle structure within which all solving takes place.
Given / Clue
A digit that is pre-filled in the puzzle at the start. Givens are fixed and cannot be changed. A typical Sudoku has between 17 and 35 givens depending on difficulty, with 17 being the proven minimum for a puzzle with a unique solution.
Band
A horizontal group of three boxes spanning the full width of the grid. There are three bands in a standard Sudoku: the top band (boxes 1-3), the middle band (boxes 4-6), and the bottom band (boxes 7-9).
Stack
A vertical group of three boxes spanning the full height of the grid. There are three stacks in a standard Sudoku: the left stack, the middle stack, and the right stack. Stacks are the vertical counterpart to bands.
Chute
A general term that refers to either a band or a stack. There are six chutes in every standard Sudoku grid: three horizontal bands and three vertical stacks.
Candidates & Notation
Terms related to tracking possible digits in cells. Notation is the bridge between basic scanning and advanced solving techniques.
Candidate
A digit that is still a valid possibility for a particular cell. When a puzzle begins, each empty cell may have several candidates. The goal of every solving technique is to reduce candidates until each cell has exactly one.
Pencil Mark
A small notation written inside a cell to track which candidates remain. Pencil marks are essential for intermediate and advanced solving because they make candidate relationships visible at a glance.
Notation
The practice of writing candidate digits in cells to aid solving. Good notation habits are the foundation of all techniques beyond basic scanning. There are multiple notation styles, each with advantages for different situations.
Snyder Notation
A minimal notation style where you only write a pencil mark when a candidate is restricted to exactly two cells within a box. This keeps the grid cleaner than full notation and is popular among speed solvers for easy and medium puzzles.
Full Candidate Notation
A notation style where every possible candidate is written in every unsolved cell. This provides complete information for applying advanced techniques but can make the grid visually dense. It is essential for hard, expert, and evil puzzles.
Elimination
The process of removing a candidate from a cell because logic proves it cannot be the solution for that cell. Every solving technique ultimately works by performing eliminations until placements become apparent.
Naked / Bare
A descriptor meaning the candidates are the only ones present in the relevant cells. For example, a naked pair consists of two cells that contain only the same two candidates and nothing else. The candidates are visible or exposed, hence the term naked.
Basic Concepts
Foundational solving concepts that every Sudoku player should know. These terms describe the simplest and most frequently used techniques.
Single
A cell whose value can be determined because only one digit is possible. Singles are the most fundamental solving step. They come in two forms: naked singles and hidden singles.
Naked Single
A cell that has only one remaining candidate after all other digits have been eliminated by row, column, and box constraints. When you find a naked single, you can immediately place that digit.
Hidden Single
A candidate that appears in only one cell within a particular row, column, or box. Even if that cell has other candidates, this digit must go there because there is no other valid position for it within that unit.
Cross-Hatching
A visual scanning technique where you trace the influence of a specific digit across rows and columns to find where it can be placed within a box. By eliminating rows and columns that already contain the digit, you narrow down its possible positions.
Scanning
The process of visually examining the grid to find placements without writing pencil marks. Scanning typically involves cross-hatching for individual digits and checking rows, columns, and boxes for singles. It is the primary technique for easy puzzles.
Constraint
A rule that limits which digits can go in a cell. In standard Sudoku, each cell is constrained by its row (no duplicate digits), its column (no duplicate digits), and its box (no duplicate digits). These three constraints are what make the puzzle solvable through logic.
Peer
Any cell that shares a unit (row, column, or box) with a given cell. Each cell has exactly 20 peers in standard Sudoku. Two peer cells cannot contain the same digit, which is the basis for all candidate eliminations.
Buddy
An alternative term for peer. Two cells are buddies if they share at least one unit (row, column, or box). Like peers, buddies cannot hold the same digit. This term is common in Sudoku forums and solving communities.
Intermediate Concepts
Concepts used in intermediate solving techniques. These terms describe patterns that emerge when candidates are analyzed within and across units.
Subset
A group of candidates that are locked into the same number of cells within a unit. If N candidates occupy exactly N cells, those cells can hold only those candidates, and all other candidates can be eliminated from those cells (hidden subset) or from the rest of the unit (naked subset).
Naked Pair
Two cells in the same unit that each contain only the same two candidates. Because those two digits must occupy those two cells, they can be eliminated as candidates from all other cells in the unit.
Hidden Pair
Two candidates that appear in only two cells within a unit. Those two cells must contain those two digits, so all other candidates in those cells can be removed. Unlike a naked pair, other candidates may obscure the pair.
Naked Triple
Three cells in a unit that together contain only three candidates (each cell has a subset of those three). The three digits are locked into those cells, so they can be eliminated from all other cells in the unit. Not every cell needs all three candidates.
Pointing Pair
When a candidate within a box is restricted to a single row or column, it is called a pointing pair (or pointing triple). Since the digit must go in that row or column within the box, it can be eliminated from the rest of that row or column outside the box.
Box/Line Reduction
The reverse of a pointing pair. When a candidate in a row or column is confined to a single box, it can be eliminated from all other cells in that box. This technique exploits the intersection between a line (row or column) and a box.
Locked Candidates
A general term covering both pointing pairs and box/line reduction. Candidates are locked when their positions in one unit restrict their positions in an intersecting unit. This is one of the most frequently used intermediate techniques.
Claim
Another name for box/line reduction. When a candidate in a row or column is found only within one box, that line claims the candidate for that box, allowing eliminations of the same candidate from other cells in the box.
Tuple
A mathematical term used in Sudoku to describe a set of N candidates locked into N cells. A pair is a 2-tuple, a triple is a 3-tuple, and a quad is a 4-tuple. Tuples can be naked (candidates only appear in those cells) or hidden (candidates only appear in those cells within the unit).
Advanced Concepts
Terms used in advanced and expert solving. These concepts involve multi-cell patterns, linked chains, and logical inference across the grid.
Fish
A family of techniques based on the intersection of rows and columns. A fish of size N involves N rows where a candidate appears in at most N columns (or vice versa). The candidate can then be eliminated from those columns outside the defining rows. Named varieties include X-Wing (size 2), Swordfish (size 3), and Jellyfish (size 4).
X-Wing
The simplest fish pattern. When a candidate appears in exactly two cells in each of two different rows, and those cells align in the same two columns, the candidate can be eliminated from all other cells in those two columns. The four cells form a rectangle, hence the name.
Swordfish
A size-3 fish pattern. When a candidate is found in at most three columns across exactly three rows, and the occupied columns are the same three, the candidate can be eliminated from those three columns outside the defining rows. It extends X-Wing logic to three rows and three columns.
Jellyfish
A size-4 fish pattern. When a candidate in four rows is restricted to the same four columns, it can be eliminated from those columns outside the defining rows. Jellyfish is rare in published puzzles but follows the same logic as X-Wing and Swordfish extended to four rows.
Fin
An extra candidate cell that prevents a fish pattern from being perfect. A finned fish can still yield eliminations, but only in cells that see both the fin and the normal elimination target. Finned X-Wings and finned Swordfish are common in harder puzzles.
Wing
A family of techniques involving a pivot cell and wing cells that create elimination opportunities. Wings use cells with two or three candidates connected through shared candidates. Common wing patterns include Y-Wing (XY-Wing) and XYZ-Wing.
Y-Wing / XY-Wing
A pattern involving three cells, each with exactly two candidates. A pivot cell shares one candidate with each of two wing cells. Any cell that can see both wing cells can have the candidate shared between the wings eliminated. The three cells form a bent chain of bivalue cells.
XYZ-Wing
An extension of the Y-Wing where the pivot cell has three candidates instead of two. The pivot shares pairs with two wing cells. The candidate common to all three cells can be eliminated from any cell that sees the pivot and both wings simultaneously.
Simple Coloring
A technique that uses two colors to mark the alternating true/false states of a candidate along a chain of conjugate pairs. If two cells with the same color can see each other, that color is false. If a cell outside the chain sees both colors, the candidate is eliminated from that cell.
Strong Link
A relationship between two cells where a candidate appears in exactly those two cells within a unit. If the candidate is not in one cell, it must be in the other. Strong links are the building blocks of chains and coloring techniques.
Weak Link
A relationship between two cells that share a unit where both contain a particular candidate, but other cells in the unit may also contain it. If the candidate is in one cell, it cannot be in the other, but both could be false. Weak links connect strong links in chains.
Chain
A sequence of cells connected by alternating strong and weak links on one or more candidates. Chains are used to prove eliminations by tracing logical implications from one end to the other. They form the basis of many expert-level techniques.
AIC (Alternating Inference Chain)
A chain that alternates between strong and weak inferences, potentially involving different candidates at each node. AICs generalize simpler techniques like X-Cycles and XY-Chains. If both ends of an AIC share a candidate and are connected by a strong inference at each end, that candidate can be eliminated from any cell that sees both endpoints.
Frequently Asked Questions
What are the most important Sudoku terms to know?
The most essential terms are cell, row, column, box (the 3x3 regions), candidate (a possible value for a cell), and elimination (removing a candidate based on logic). Understanding these basics is enough to start solving easy puzzles. As you tackle harder puzzles, terms like naked pair, hidden single, and X-Wing become important.
What is the difference between a naked single and a hidden single?
A naked single is a cell that has only one remaining candidate after all other digits have been eliminated. A hidden single is a candidate that appears in only one cell within a row, column, or box, even though that cell may still have other candidates listed. Both result in placing a digit, but they are identified differently.
What does 'candidate' mean in Sudoku?
A candidate is a digit (1 through 9) that could potentially be placed in a given cell based on the current state of the puzzle. As you solve the puzzle and apply techniques, candidates are eliminated from cells until only one remains, at which point the digit can be placed.
What are fish patterns in Sudoku?
Fish patterns are a family of advanced Sudoku techniques named after aquatic creatures. They include X-Wing (2 rows/columns), Swordfish (3 rows/columns), and Jellyfish (4 rows/columns). Each pattern involves a candidate that is restricted to the same set of columns within certain rows (or vice versa), allowing eliminations in those columns outside the defining rows.
Ready to Apply These Terms?
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