Whether you just started learning Sudoku or you are diving into advanced strategy guides, encountering unfamiliar terms can be frustrating. This guide covers every important Sudoku term in plain language, organized from basics to advanced concepts. Think of it as a narrative companion to the glossary - less dictionary, more explanation.
Before learning any solving technique, you need to understand the parts of the Sudoku grid. A cell is a single square in the grid - a standard 9x9 grid has 81 cells. A row is a horizontal line of 9 cells, a column is a vertical line of 9 cells, and a box (also called block or region) is one of the nine 3x3 sub-grids. A house is a general term for any row, column, or box. A given (or clue) is a number pre-filled in the puzzle at the start. The grid is the entire 9x9 playing field consisting of 81 cells organized into 9 rows, 9 columns, and 9 boxes.
These terms describe the fundamental actions and concepts of Sudoku solving. A candidate is any digit that could potentially be placed in a cell based on what numbers are already present. A pencil mark is the physical notation of that candidate written in the cell. Elimination is the act of removing a candidate because logic proves it cannot go there. Crosshatching is a visual scanning technique where you check which numbers are blocked in a box by its intersecting rows and columns. A naked single is when a cell has been reduced to a single candidate. A hidden single is when a candidate appears in only one cell within a house. A conjugate pair refers to two cells within a house that are the only two places a particular candidate can go.
Sudoku terminology builds on itself logically. Cells are organized into houses (rows, columns, and boxes). Each empty cell has candidates - the numbers that could go there. You write these as pencil marks. Solving means performing eliminations - using logic to remove candidates until each cell has just one. A naked single is a cell with one candidate remaining. A hidden single is a candidate with only one possible cell in its house. Naked pairs, pointing pairs, and X-Wings are all patterns that let you eliminate candidates from cells that are not directly involved in the pattern.
These terms appear in guides for hard, expert, and evil-rated puzzles. A naked pair is two cells in the same house that share exactly the same two candidates. A hidden pair is two candidates that only appear in the same two cells within a house. A pointing pair occurs when a candidate in a box is restricted to a single row or column. Box/line reduction is the complement of a pointing pair. An X-Wing is a pattern where a candidate appears in exactly two cells in each of two rows aligned on the same two columns. Swordfish extends this to three rows and columns. Coloring uses conjugate pairs with alternating colors to find eliminations. Forcing chains assume a value and follow logical consequences. Unique rectangles exploit the rule that a valid puzzle has exactly one solution.
These terms appear in discussions about Sudoku construction, mathematics, and variants. A Latin Square is an n x n grid where each symbol appears exactly once per row and column. Symmetry refers to symmetrically placed givens in published puzzles. A proper puzzle has exactly one valid solution - the minimum number of givens for a proper puzzle is 17. Brute force means solving by systematically trying every possibility. A band is a group of three rows sharing the same three boxes, while a stack is the column equivalent. A peer is any cell that shares a house with a given cell - each cell has exactly 20 peers.
Now that you understand the vocabulary, you are ready to deepen your Sudoku knowledge. Browse the interactive glossary for quick-reference definitions. Study each technique in detail on the strategies page. Use the cheat sheet as a solving companion. Practice with free puzzles at every difficulty level.
A house is any complete group of 9 cells that must contain the digits 1 through 9 exactly once. In standard Sudoku, there are 27 houses: 9 rows, 9 columns, and 9 boxes (3x3 regions). The term is used as a convenient shorthand when a rule or technique applies to rows, columns, and boxes equally.
A candidate is any number that could potentially go in a cell based on the current state of the puzzle. A pencil mark is the physical notation of that candidate - a small number written in the cell as a reminder. All pencil marks represent candidates, but you might not write pencil marks for every candidate, especially in easy puzzles.
Elimination is the process of removing a candidate from a cell because logic proves it cannot go there. For example, if a 5 already exists in a row, you can eliminate 5 as a candidate from every other cell in that row. All Sudoku solving techniques are fundamentally elimination techniques.
A naked pair is two cells in the same house that contain exactly the same two candidates and nothing else. A hidden pair is two candidates that appear in only two cells within a house, but those cells may also contain other candidates. In a naked pair, you eliminate those two numbers from other cells. In a hidden pair, you eliminate the other numbers from those two cells.
Crosshatching is a visual scanning technique where you look at a box and check which numbers are already present in the rows and columns that pass through it. By crossing out impossible placements, you can often find where a number must go within that box. It is one of the first techniques beginners learn.
A given (also called a clue) is a number that is pre-filled in the puzzle grid at the start. These are the numbers you cannot change. The number of givens determines much of the puzzle's difficulty - easy puzzles have more givens (typically 36 to 45), while expert puzzles have fewer (22 to 27).
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