Sudoku Glossary

Every sudoku term explained simply. A dictionary to help you follow the guides and talk like an expert.

Grid

The full sudoku board, made up of 81 cells arranged in 9 rows and 9 columns.

Cell

Each of the 81 spots on the grid where a number from 1 to 9 goes.

Row

One of the 9 horizontal lines on the board. It must contain the numbers 1 to 9 without repeats.

Column

One of the 9 vertical lines on the board. It must also contain 1 to 9 without repeats.

Block (or region, or box)

Each of the 9 3x3 squares the board is divided into. Just like rows and columns, it can't repeat any number.

Clue

Each number already placed at the start of the game. The fewer clues, the harder the sudoku tends to be.

Candidate

A number that could still go in an empty cell because it doesn't break any rule. Solving a sudoku is about eliminating candidates.

Notes (or pencil mode)

Small numbers jotted in a cell to remember its possible candidates. Learn to use them in the guide on how to use notes mode.

Scanning

The basic technique of going through rows, columns and blocks looking for where a number can only go in one spot. It's the first method every player learns.

Single candidate

When a cell has only one possible number left, or when a number can only go in one cell of its row, column or block. The most direct deduction.

Naked pair

Two cells in the same row, column or block that only allow the same two candidates. That lets you eliminate those numbers from the rest of the group.

Naked triple

The same idea as a naked pair, but with three cells sharing the same three candidates.

Hidden pair

Two candidates that only appear in two cells of a group, even if those cells also have other candidates that can be eliminated.

X-Wing

An advanced technique based on a rectangular pattern: when a candidate is confined to the same two columns in two rows (or vice versa), it can be eliminated from other cells. Explained in advanced techniques.

Unique solution

A well-built sudoku has only one way to be completed. That's why it can always be solved through logic, without guessing.

Backtracking

The "try and backtrack" method computers use to generate and solve sudokus. Find out how it works in how sudokus are generated.

Difficulty level

The sudoku's category (Easy, Medium, Hard or Expert). It depends not just on the clues, but on which techniques are needed to solve it.

Conflict

An error where the same number appears twice in the same row, column or block. It signals that some cell is wrong.