Sudoku Terminology

These are some of the terms used here on SudokuMix.

Note: You won’t find explanations for the different sudoku variants; you’ll find that in the rules.


A collection of cells, marked by a thicker outline. As with rows and columns, no number can be repeated in a box.

In standard sudoku, which measures 9 × 9 cells, the boxes are 3 × 3 cells. Another common variant is sudoku for kids, which measures 6 × 6 cells with boxes measuring 3 × 2 cells.

Here on SudokuMix we love using irregular boxes. Such puzzles are called jigsaw sudoku, because the boxes resemble jigsaw puzzle pieces.


Numbers that may be the correct number in a cell.

We use pencil marks to keep track of candidates.


The smallest unit of a sudoku puzzle. A standard sudoku puzzle consists of 9 × 9 cells.


A whole, vertical stack of cells.


A row of cells going diagonally from one corner of a puzzle to the opposite.

In X-sudoku puzzles the diagonals must also adhere to the rule of no repeated numbers.

In SudokuMix X-sudoku puzzles, such diagonals are marked by thin, gray lines.

Some puzzles may have more than one diagonal in each direction. Even though these diagonals are shorter, and thus can’t contain all the puzzle’s numbers, the rule of no repeated number still applies.


The given (visible) numbers in an unsolved puzzle. In standard sudoku puzzles, they are the only keys to solving the puzzle, and it’s been proven that you need at least 17 givens to solve a standard sudoku.

In other sudoku variants, there might be fewer givens, or none at all, and you’ll have to use the extra rules to deduce where the numbers go and how to solve the puzzle.


A collection of cells in which no number can be repeated.

  • Standard sudoku puzzles have three kinds of groups: rows, columns, and boxes.
  • In X-sudoku puzzles, the two diagonals are extra groups.
  • Other variants might have extra groups—often marked by shaded cells.


Puzzles where the boxes have irregular shapes.


When there are only two candidates for two cells in the same group, it’s called a pair.

Naked pair

A pair is naked when all other candidates have been eliminated from the two cells. The two numbers can then be eliminated from other cells in the same group.

Hidden pair

A pair is hidden when there are other candidates in the two cells. The other candidates can be eliminated from the two cells.

Pencil marks

Candidates of a cell, marked by small numbers. We recommend that the numbers are written in a grid with the numbers always in the same position. This makes it easier to recognize patterns in the numbers.


A whole, horizontal row of cells.


See diagonal.

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