📖 Glossary
Sudoku Terms — A Friendly Glossary
Sudoku puzzlers use a lot of funny-sounding words — "naked singles", "pointing pairs", "X-Wings". Don't worry, none of them are as scary as they sound!
This page is a kid-friendly glossary of the most common sudoku terms. Each word has a simple meaning and a quick example, grouped into sections so you can find what you need fast.
What you will learn
The board
First, the parts of the grid. Every sudoku puzzle uses these pieces.
- Sudoku / soo-DOH-koo /
- A number puzzle where you fill a grid so every row, column and box uses every number exactly once. The word is Japanese and means "single number".
★ A classic sudoku uses the numbers 1 to 9 on a 9×9 grid.
- Grid
- The whole square puzzle. A classic sudoku grid is 9 squares wide and 9 squares tall, making 81 squares in total.
- Cell
- One little square on the grid. You put exactly one number in each cell.
★ A 9×9 grid has 81 cells.
- Row
- A line of cells that goes straight across the grid, left to right. A 9×9 grid has 9 rows.
- Column
- A line of cells that goes straight up and down the grid. A 9×9 grid has 9 columns.
- Box (or region)
- A smaller square made of 3×3 cells (9 cells) inside the big grid. A 9×9 sudoku has 9 boxes. Each box must also use every number once.
★ On a 4×4 puzzle the boxes are 2×2. On a 6×6 puzzle the boxes are 2×3.
- Unit
- A grown-up word for any row, any column or any box — basically any group of cells that must contain every number once.
Numbers & clues
The numbers you start with and the ones you fill in.
- Given (or clue)
- A number that is already printed in the grid when the puzzle starts. You cannot change or remove a given.
★ Easy puzzles have lots of givens; hard puzzles have very few.
- Candidate (or possible)
- A number that might belong in an empty cell. Good players write small candidates in the corner of a cell while they think.
- Pencil marks (or notes)
- The little candidate numbers you jot in a cell to remember your options. In our games, tap the Notes button to switch pencil-mark mode on.
- Solution
- The finished puzzle — every cell filled correctly. A good sudoku has just one solution.
- Unique solution
- A puzzle where there is only one correct way to finish. Real sudoku puzzles always have a unique solution.
Smart techniques
The tricks sudoku players use to find the next number. Try them the next time you play!
- Naked single
- A cell with only one candidate left. If 1–8 are already in the row, column or box, the only number that fits is 9. That 9 is a naked single.
★ Naked singles are the first trick new players learn.
- Hidden single
- A number that can only go in one cell of a row, column or box — even if that cell has other candidates too. You have to look carefully to spot it.
- Naked pair
- Two cells in the same row, column or box that share the exact same two candidates. Those two numbers can be erased from all other cells in the unit.
★ If cells A and B both only hold {3, 7}, no other cell in that row can be a 3 or a 7.
- Pointing pair
- Inside one box, a candidate number fits in only two cells — and those cells sit in the same row or column. That means the number can't go anywhere else in that row or column outside the box.
- X-Wing
- A tricky pattern where the same candidate appears in exactly two cells in two different rows, and those cells line up in the same two columns. The candidate can be erased from the rest of those columns.
- Elimination
- Ruling out a number from a cell because it already appears in the same row, column or box. Elimination is the heart of every sudoku trick.
- Backtracking
- A way computers solve sudoku by trying a number, moving on, and stepping back if it leads to a dead end. Sudoku solvers use backtracking.
- Scanning
- Looking across rows, down columns and inside boxes to see where a number can and cannot go. Scanning is how most kids find their first answers.
Puzzle types
The different sudoku puzzles you can play on this site.
- Classic Sudoku
- The normal 9×9 puzzle with 3×3 boxes. Fill the grid with 1–9 so each row, column and box has every number once.
- 4×4 Sudoku
- A tiny 16-cell grid using the numbers 1–4. Perfect for first-time puzzlers and young kids.
- 6×6 Sudoku
- A 36-cell grid using the numbers 1–6, with 2×3 boxes. A friendly step between 4×4 and the classic 9×9.
- Killer Sudoku
- A sudoku puzzle with dashed "cages" that must add up to a target number. You need sudoku rules plus a little bit of adding.
- Jigsaw Sudoku
- A 9×9 sudoku where the 9 boxes are wiggly jigsaw shapes instead of neat 3×3 squares. Rows and columns still work the same way.
- Cage
- A group of cells outlined with a dashed line in killer sudoku. The numbers in a cage must add up to the little number printed in its corner.
Buttons & help
The helpers on our game board and what they do.
- Hint
- A helping hand that fills in the right number for the cell you have selected. Hints are great when you get stuck.
- Check
- A button that spots any mistakes so far. Great for a quick look before you carry on.
- Undo
- Steps back to the last move. If you change your mind or make a slip, tap Undo.
- Auto Notes
- Fills in all the candidate pencil marks for every empty cell at once. Saves time on harder puzzles.
- Solver
- A tool that finishes a sudoku for you. Try our free sudoku solver if you want to check an answer or get past a tricky spot.
Quick questions
What does the word "sudoku" mean?
Sudoku is a Japanese word. It comes from "sūji wa dokushin ni kagiru", which means "the digits must be single". In short: every number can only appear once in each row, column and box.
Why is it called a "naked" single?
Because the answer is out in the open — only one candidate is left in the cell, with nothing hiding it. A "hidden" single is trickier because it is mixed in with other candidates.
Do kids need to learn all these terms?
Not at all! Kids can enjoy sudoku without knowing any fancy words. This glossary is here for when you are curious or want to talk about puzzles with friends.
What is the difference between a clue and a candidate?
A clue (or given) is a number already printed on the puzzle when you start — you cannot change it. A candidate is a number you think might work in an empty cell.
Where can I use these words?
Anywhere you play sudoku! They are the same words grown-ups use, whether in newspapers, books, apps or online puzzles. You will see them pop up in our tips articles, too.
Keep learning
The best way to learn these words is to play! Try an easy puzzle and see how many terms you can spot — naked singles, scanning, pencil marks. The more you play, the more the language of sudoku starts to feel natural.