Sudoku has its own vocabulary, and it is not always explained. Here are the terms you will meet in the tutorials and in the books, defined in a sentence or two, each linking to the article that develops it.
Bivalue cell
A cell left with only two candidates. These cells are the starting point of many elaborate techniques, from the Y-Wing to the W-Wing.
See the tutorial →Box
One of the nine 3×3 squares making up the grid. Each box must contain the digits 1 to 9, once each.
See the tutorial →Box Reduction
When every possible location of a digit on a row fits inside a single box, that digit is eliminated from the rest of that box. It is the mirror of the Pointing Pair.
See the tutorial →Candidate
A digit still possible in a given cell, given what is already placed in its row, column and box. Writing them down is not cheating: without them most techniques are invisible.
See the tutorial →Column
One of the nine vertical lines of the grid. Each column must contain the digits 1 to 9, once each.
See the tutorial →Fin
The surplus candidate or candidates that stop a pattern from being a perfect X-Wing. To be usable, the fin must sit entirely inside one box, the one holding the corner concerned.
See the tutorial →Given
A digit printed at the start, which cannot be changed. Also called a clue. Their number gives a first idea of the difficulty without determining it.
Jellyfish
The extension of the Swordfish to four rows and four columns. The principle is identical, but the pattern is far rarer and much harder to spot by eye.
Naked pair
Two cells of the same unit holding exactly the same two candidates and nothing else. Those two digits are reserved for them and vanish from the other cells of the unit.
See the tutorial →Naked single
A cell left with a single candidate, so the digit is determined. It is the most elementary technique, and the one that unlocks the end of most grids.
Naked triple
Three cells of the same unit whose pooled candidates amount to only three digits. No cell needs to carry all three, which is the most widespread error on this technique.
See the tutorial →Pincer
In a Y-Wing or an XYZ-Wing, one of the two bivalue cells that see the pivot. They are the ones carrying the digit to be eliminated.
See the tutorial →Pivot
The central cell of a Y-Wing or an XYZ-Wing, the one both pincers see. It holds two candidates in a Y-Wing, three in an XYZ-Wing, and that difference changes the elimination rule.
See the tutorial →Pointing Pair
When every possible location of a digit inside a box lines up on the same row or column, that digit is eliminated from the rest of that row or column, outside the box.
See the tutorial →Row
One of the nine horizontal lines of the grid. Each row must contain the digits 1 to 9, once each.
See the tutorial →Sashimi X-Wing
An X-Wing missing one corner, replaced by a fin sitting in the box of the absent corner. Eliminations are confined to the intersection of the column and that box.
See the tutorial →Scanning
The simplest method: sweeping the rows and columns of a digit to see where it cannot go, until only one cell is left available in a box.
See the tutorial →See (to)
Two cells see each other if they share a row, a column or a box. A cell sees 20 others. This notion governs every elimination in the elaborate techniques.
See the tutorial →Strong link
Also called a conjugate pair: a digit left with only two possible locations within one unit. One of the two must take it, and that certainty is what makes the W-Wing work.
See the tutorial →Swordfish
The extension of the X-Wing to three rows and three columns. No row needs three locations: all that counts is the union of the columns, which must not exceed three.
See the tutorial →Unit
Generic term for a row, a column or a box. A grid has 27 units, and every basic technique reasons inside a single one of them.
See the tutorial →W-Wing
Two identical bivalue cells that do not see each other, connected by a strong link on one of their two digits. The other digit is eliminated from the cells seeing both bivalues.
See the tutorial →X-Wing
A digit whose locations on two rows fall in the same two columns. It is then eliminated from the rest of those two columns. The first of the fish techniques.
See the tutorial →XYZ-Wing
A Y-Wing whose pivot holds three candidates. Since the pivot may itself be the targeted digit, the cleaned cells must see all three cells, not just the two pincers.
See the tutorial →Y-Wing
A bivalue pivot and two bivalue pincers that see it, sharing a common digit. That digit is eliminated from the cells seeing both pincers.
See the tutorial →📘 Go further with the Domino33 books
Every technique on this site is covered step by step in the Domino33 memento, available in English.
