Sudoku Terminology Glossary
Welcome to our comprehensive Sudoku glossary, your ultimate reference guide for mastering the language of the grid. Whether you are a beginner learning basic board anatomy or an intermediate solver looking to decode advanced logic from our walkthroughs, this page breaks down every essential concept into clear, actionable definitions. Understanding this terminology is the first step toward moving past guesswork and training your eyes to spot the hidden patterns that unlock complex puzzles.
The logical categories for the terminology range from the fundamental components of the board to elite solving strategies. As you explore our step-by-step tutorials across the site, use this glossary to quickly look up unfamiliar terms, cross-reference techniques, and solidify your foundational knowledge. Bookmark this page so you can easily pull it up whenever you find your current puzzle grind coming to a halt.
Sudoku Terminology Categories:
Grid Anatomy
Grid
The entire 9×9 playing board consisting of 81 individual squares.
Cell
A single individual square on the grid that holds one digit from 1 to 9.
Row
A horizontal line of 9 cells. Rows are traditionally numbered 1 through 9 from top to bottom.
Column
A vertical line of 9 cells. Columns are traditionally numbered 1 through 9 from left to right.
Box (Block / Subgrid)
One of the nine smaller 3×3 regions outlined by thicker borders on the grid, each containing 9 cells.
House (Unit)
A collective term for any single valid group of 9 cells—meaning any Row, Column, or Box. Every house must ultimately contain the numbers 1 through 9 without repetition.
Given (Clue)
A number that is pre-filled into the grid at the start of the puzzle by the creator. Givens cannot be changed or moved.
Notation & Markings
Candidate
A number that could theoretically and legally fit into a specific empty cell according to basic Sudoku rules.
Pencil Marks (Notes)
Small placeholder numbers written inside an empty cell to keep track of remaining viable candidates. Common styles include “Snyder Notation” (marking candidates only when they have exactly two spots left in a box) and “Full Notation”.
Coordinates (RC Notation)
The standard mapping system used to identify a specific cell on the grid. “R” stands for row and “C” stands for column. For example, r3c5 refers to the cell located at Row 3, Column 5.
Basic & Intermediate Techniques
Elimination
The logical process of crossing out specific candidate numbers from a cell’s pencil marks because that number already appears somewhere else in its intersecting row, column, or box.
Naked Single
An empty cell where exactly one candidate remains possible. Because all other 8 digits have been eliminated, that remaining candidate must be the answer.
Hidden Single
A scenario where a specific candidate can only fit into one single cell within a particular house (row, column, or box), even if that specific cell still has other potential candidates listed in it.
Subsets (Naked Pairs / Triplets / Quads)
A group of N cells within the same house that collectively contain exactly N candidates. For example, a Naked Pair occurs when two cells in a row only contain the same two candidates. This locks those digits into those two cells, allowing you to safely eliminate them from all other cells in that row.
Locked Candidates (Pointing / Claiming)
When all possible locations for a candidate within a box are restricted to a single row or column, that candidate is “pointing.” You can eliminate that candidate from the rest of that entire row or column outside of that specific box.
Advanced Logic & Strategies
X-Wing
An advanced pattern involving four cells that form a rectangle across two parallel rows and two parallel columns. If a specific candidate is restricted to exactly two cells in each of those rows, and those cells share the same columns, you can eliminate that candidate from all other cells in those columns.
Swordfish
An extension of the X-Wing pattern that spans three rows and three columns. When a candidate is restricted to at most three cells in three distinct rows, and those cells align perfectly across three columns, the candidate can be eliminated from those columns everywhere else.
Forcing Chain
A continuous sequence of logical “if/then” links tracking candidates across multiple cells. If testing a candidate as either true or false leads to the exact same deduction further down the chain, that deduction is proven to be absolute fact.
Core Puzzle Concepts
Proper Sudoku
A mathematically sound Sudoku puzzle that is guaranteed to have exactly one unique solution, achievable strictly through logical deduction without any reliance on blind guessing.
Bifurcation (Guessing)
The practice of picking a cell with two candidates, randomly choosing one, and continuing the puzzle to see if it results in an error. While functional, it is generally discouraged in logical Sudoku solving tutorials.
Symmetry
The geometric design of the initial given clues on the board. Most premium hand-crafted puzzles exhibit rotational symmetry (e.g., turning the puzzle 180 degrees yields the exact same pattern of clues).