House
One of the nine 3×3 boxes in the grid. Each house must contain digits 1-9 exactly once. Rows, columns, and houses together are called units.
Also called: box, block, nonet
Reference
Sudoku Glossary
Essential terms and definitions for understanding Sudoku solving techniques. Bookmark this page for quick reference while learning!
1
Grid Structure
Line
A row or column spanning the entire 9×9 grid. Each line must contain digits 1-9 exactly once.
Lines can be horizontal (rows) or vertical (columns)
Cell
An individual square within the 9×9 grid where a single digit will be placed. Each cell belongs to exactly one row, one column, and one house.
Also called: square, position
2
Solving Methods
Candidates
The possible numbers that could be placed in a cell based on current constraints. As the puzzle progresses, candidates are eliminated until only one remains.
Also called: possibilities, options
Pencil Marks
Small notation showing which candidates are possible in each cell. Essential for tracking possibilities and applying advanced techniques.
Also called: notation, candidate marks
Elimination
The process of removing impossible candidates from cells based on Sudoku constraints and logical deductions.
The core mechanism of most solving techniques
Given
A number that is already placed in the puzzle at the start. Givens provide the initial constraints that make the puzzle solvable.
Also called: clue, starting number
3
Technique Categories
Singles
Techniques that identify cells where only one number can be placed. The foundation of all Sudoku solving.
- Naked Single
- A cell with only one candidate remaining
- Hidden Single
- A number that can only go in one place within a row, column, or house
Intersection
Techniques that use the overlap between a house and a row or column to make eliminations.
- Locked Candidates
- When candidates are confined to specific intersections
- Pointing/Claiming
- Specific types of locked candidate patterns
Sets
Techniques based on groups of cells that share the same limited candidates.
- Naked Sets
- When cells contain the same visible candidates
- Hidden Sets
- When numbers are confined to the same group of cells
Fish Patterns
Advanced techniques based on rectangular arrangements of candidates.
- X-Wing
- 2×2 fish pattern
- Swordfish
- 3×3 fish pattern
- Jellyfish
- 4×4 fish pattern
Notation
Quick Reference
Common Abbreviations
- R1C1
- Row 1, Column 1
- B1
- Box 1 (top-left)
- {1,2,3}
- Candidate set notation
Grid Numbering
- Rows numbered 1-9 from top to bottom
- Columns numbered 1-9 from left to right
- Boxes numbered 1-9 from top-left to bottom-right
Start Learning
Ready to apply these terms? Begin your Sudoku journey with our structured lessons.