Glossary

Quick reference for Sudoku terminology.

A

Arrow Sudoku: Variant where circled cells equal the sum of cells along their arrows.

Auto-notes: Feature that automatically fills in candidate pencil marks based on current constraints.

B

Bifurcation: Trial-and-error technique of assuming a value and checking for contradictions. Also called "guessing" or "trial."

Bi-value cell: A cell with exactly two candidates.

Box: One of the nine 3×3 regions in the grid. Also called block, region, or house.

Box/Line Reduction: Technique where row/column constraints eliminate candidates within a box.

C

Candidate: A number that could potentially go in a cell. Also called possibility.

Cell: One of the 81 squares in the grid.

Chain: A sequence of linked cells used in advanced solving techniques.

Clue: See Given.

Column: A vertical line of 9 cells.

Conflict: When the same number appears twice in a row, column, or box.

Cross-hatching: Scanning technique that mentally crosses out rows and columns to find valid cells for a digit.

D

Diagonal Sudoku: Variant where both main diagonals must also contain 1-9 without repetition. Also called Sudoku X.

E

Elimination: Removing a candidate from a cell's possibilities.

Empty Rectangle: Advanced technique using a box with candidates forming an L or T shape.

F

Finned X-Wing: An X-Wing pattern with an extra candidate cell (the "fin") that limits eliminations.

Fish: Family of techniques (X-Wing, Swordfish, Jellyfish) based on row/column candidate patterns.

G

Given: A number pre-filled in the puzzle. Also called clue.

Grid: The complete 9×9 Sudoku board.

H

Hidden pair/triple/quad: Pattern where candidates appear in only a limited number of cells within a unit, even if those cells have other candidates.

House: General term for any row, column, or box (a "unit").

J

Jellyfish: Advanced fish technique using 4 rows and 4 columns.

K

Killer Sudoku: Variant with cages showing sums instead of given digits.

L

Latin Square: Mathematical structure where each symbol appears once per row and column. Sudoku adds the box constraint.

Link: Connection between cells in chain-based techniques. See Strong link, Weak link.

N

Naked pair/triple/quad: Pattern where cells contain only candidates from a specific set, with no other candidates.

Notes: Small numbers written in cells to track candidates. Also called pencil marks.

P

Peer cells: All cells that share a row, column, or box with a given cell. Each cell has 20 peers.

Pencil marks: See Notes.

Pivot: In XY-Wing, the central cell that connects both wing cells.

Pointing pair/triple: Pattern where a candidate in a box is restricted to one row or column, eliminating that candidate from the rest of that row/column.

Q

Quad: Four cells sharing four candidates. Can be naked (cells have only those four) or hidden (candidates appear only in those four cells).

R

Remote Pairs: Chain of bi-value cells with the same two candidates, alternating along the chain.

Row: A horizontal line of 9 cells.

S

Sandwich Sudoku: Variant where clues indicate sums of digits between 1 and 9 in rows/columns.

Scanning: Basic technique of checking rows, columns, and boxes for placement opportunities.

Single: A cell where only one number is possible. Can be naked (one candidate) or hidden (only place for a digit in a unit).

Skyscraper: Two-row pattern with offset strong links, similar to a bent X-Wing.

Strong link: When a candidate appears in exactly two cells of a unit—if one is false, the other must be true.

Swordfish: Advanced fish technique using 3 rows and 3 columns.

T

Thermo Sudoku: Variant with thermometer shapes where digits must increase from bulb to tip.

Triple: Three cells sharing three candidates. Can be naked or hidden.

Turbot Fish: Family of single-digit chain techniques including Skyscraper and 2-String Kite.

U

Undo: Reverse your last action.

Unique Rectangle: Technique that avoids deadly patterns which would create multiple solutions.

Unit: A row, column, or box—any group that must contain 1-9.

W

W-Wing: Four-cell pattern using bi-value cells and a strong link to make eliminations.

Weak link: Connection where if one cell has a candidate, the other cannot (because they share a unit).

Wing: In XY-Wing patterns, the two cells connected to the pivot that share a common candidate.

X

X-Chain: Chain of strong and weak links on a single candidate.

X-Wing: Advanced technique using 2 rows and 2 columns in a rectangle pattern, where a candidate appears in exactly those 4 corners.

XY-Chain: Chain of bi-value cells where each cell shares one candidate with the next.

XY-Wing: Advanced technique using three bi-value cells—a pivot and two wings—to eliminate a shared candidate.