Reference
The words sudoku uses.
Sudoku doesn't have many terms, but it uses them precisely. A unit isn't just a box, and a strong link doesn't mean "look harder". Every technique page on this site uses these words exactly as defined here.
The basics
The words you meet first.
- Given
- A digit printed in the puzzle before you start. Also called a clue.
- Cell
- One of the 81 squares. A cell is named by its row and column, and it belongs to exactly one row, one column and one box.
- Unit
- A row, a column or a box: nine cells that between them must hold every digit once.
- Peers
- The twenty cells that share a unit with a given cell: eight in its row, eight in its column and four more in its box, after the overlaps are counted once. A digit placed in a cell removes itself from all twenty.
- Candidate
- A digit a cell could still take. Written into a cell as a small mark, it's called a pencil mark.
- Single candidate
- A cell with exactly one candidate left. Also called a naked single. It's the one move that needs nothing but counting.
- Hidden single
- A digit with exactly one possible cell left in a unit, even though that cell can also take others.
Advanced
The words the harder techniques use.
- House
- Another word for unit, common in older sudoku guides: any row, column or box. This site says unit.
- Boxrow / boxcol
- The three cells a box shares with one row or one column. A pointing elimination travels along a boxrow.
- Candidate list
- Every digit a cell can still take, written in the cell as pencil marks. A technique that removes candidates needs this list to be complete and correct.
- Elimination
- Crossing a digit off a cell's candidates without placing anything. Most techniques past the beginner ones work this way.
- Fish
- The family of techniques built from one digit that has a fixed number of homes across a set of rows or columns: X-Wing, swordfish, jellyfish and the finned variants of each.
- Wing
- The family built from three cells holding three digits between them, where one cell forces another: XY-Wing, XYZ-Wing and W-Wing.
- Pivot and pincer
- The two parts of a wing. The pivot is the cell that sees both others; the pincers are the cells it forces. Older guides call the pincers wings.
- Strong link
- A relationship where two candidates can't both be false: if one isn't the digit, the other must be. Two cells that are the only homes for a digit in a unit are strongly linked.
- Weak link
- A relationship where two candidates can't both be true: two cells in the same unit can't both hold the same digit. Every strong link is also a weak one.
- Chaining technique
- Any technique that follows strong and weak links around the grid to prove a candidate impossible. X-Chains, XY-Chains and colouring are all chaining techniques.
- Uniqueness technique
- A technique that uses the puzzle having exactly one solution, rather than the grid alone. Unique rectangles and BUG are the common examples.
- Finned
- A fish with one extra possible cell, the fin, which spoils the clean pattern but still allows a narrower elimination. Finned X-Wing and finned swordfish are the usual ones.
Using them
Where each word turns up.
The first two techniques only need cells, units and candidates. Pairs and triples add eliminations. The advanced pages go further: X-Wing is where you start tracking one digit across lines, XY-Wing introduces pivots and pincers, and unique rectangles use the fact that a puzzle has only one solution.
New to sudoku? The first-puzzle walkthrough only uses the first couple of these.