Sudoku Glossary
Grid / Board
The entire 9×9 playing area, containing 81 cells.
Row
A horizontal line of 9 cells. There are 9 rows, numbered 1-9 from top to bottom. Each row must contain digits 1-9 exactly once.
Column
A vertical line of 9 cells. There are 9 columns, numbered 1-9 from left to right. Each column must contain digits 1-9 exactly once.
Box / Block
A 3×3 region outlined with thicker borders. There are 9 boxes. Each box must contain digits 1-9 exactly once. Rows, columns, and boxes are the three fundamental units of Sudoku.
Cell
The smallest unit of the grid. Each cell holds one digit from 1-9.
Given / Clue
A pre-filled digit at the start of a puzzle. These cannot be changed and serve as the starting point for logical deduction.
Candidate / Pencil Mark
Possible digits that could go in a cell, usually noted in small writing. Narrowing down candidates is the key to solving.
Unique Solution
A hallmark of a proper Sudoku — exactly one way to fill the grid that satisfies all rules. All puzzles on this site are verified to have a unique solution.
Naked Single
A cell with only one remaining candidate. The simplest solving technique — just fill it in.
Hidden Single
When a digit can only go in one specific cell within a row, column, or box. Looking at the grid from the digit's perspective.
Pair
Two cells in the same unit that share the same two candidates. Comes in naked pair and hidden pair varieties.
Elimination
The process of removing impossible digits from candidates. The essence of Sudoku solving.
Box-Line Reduction
An elimination technique that leverages the relationship between a box and a row or column.
Swordfish
An advanced technique that extends X-Wing across three rows and three columns. Used to clean up the board.
Tip: Click "Techniques" in the navigation to see detailed explanations of each solving technique, including step-by-step examples and common mistakes.