Question 1

Candidate

Accepted Answer

A digit that could legally go in a cell given the current row, column and box constraints. Also called a pencil mark.

Question 2

Given (Clue)

Accepted Answer

A digit printed in the puzzle at the start. Givens cannot be changed and define the unique solution.

Question 3

Unit

Accepted Answer

Any group of cells that must contain each digit exactly once — a row, a column, or a box (and the diagonals in Sudoku X).

Question 4

Box

Accepted Answer

A 3×3 region of a classic grid (2×3 in 6×6, 2×2 in 4×4) that must contain each digit once.

Question 5

Naked Single

Accepted Answer

A cell with only one remaining candidate, which must therefore be its value.

Question 6

Hidden Single

Accepted Answer

A digit that can be placed in only one cell of a unit, even if that cell shows other candidates.

Question 7

Bi-value Cell

Accepted Answer

A cell with exactly two candidates. Bi-value cells are the building blocks of wings and chains.

Question 8

Strong Link

Accepted Answer

A unit in which a digit has exactly two candidate cells: if one is false the other must be true. The basis of coloring and chains.

Question 9

Locked Candidate

Accepted Answer

A digit confined to the intersection of a box and a line, enabling pointing-pair or box/line-reduction eliminations.

Question 10

Fish

Accepted Answer

A family of single-digit patterns (X-Wing, Swordfish, Jellyfish) defined over N rows and N columns.

Question 11

Pencil Marks

Accepted Answer

Small candidate notes written into a cell to track which digits remain possible. See Snyder notation for an efficient scheme.

Question 12

Uniqueness

Accepted Answer

The property that a valid puzzle has exactly one solution. Unique-rectangle and BUG techniques exploit it.

Question 13

Conjugate Pair

Accepted Answer

A unit in which a digit has exactly two candidate cells, so one of them must be that digit. Conjugate pairs are the strong links that colouring, skyscrapers and W-Wings are built from.

Question 14

Pivot

Accepted Answer

The hinge cell of a wing: in an XY-Wing it is the bi-value cell that sees both pincers; in an XYZ-Wing it carries three candidates and is also part of the elimination.

Question 15

Pincer

Accepted Answer

One of the two outer cells of a wing. Whichever value the pivot takes, one pincer is forced to a shared digit, eliminating it from cells the pincers both see.

Question 16

Chain

Accepted Answer

A sequence of cells linked by alternating strong and weak inferences. Following the chain forces a digit on or off at its ends, the basis of forcing chains and remote pairs.

Question 17

Cross-hatching

Accepted Answer

Scanning the rows and columns that already contain a digit to see which cell of a box is left for it — the fastest way to find hidden singles.

Question 18

Naked Subset

Accepted Answer

A group of N cells in a unit whose combined candidates total exactly N digits (pair, triple or quad), locking those digits out of the rest of the unit.

Question 19

Hidden Subset

Accepted Answer

N digits restricted to the same N cells of a unit (pair, triple or quad), so every other candidate can be erased from those cells.

Question 20

Deadly Pattern

Accepted Answer

A candidate arrangement that would allow two different solutions. Because a real puzzle is unique, such a pattern can never complete — uniqueness techniques eliminate the candidate that would create it.

Question 21

Cage

Accepted Answer

In Killer Sudoku, a dotted group of cells with a target sum. Its digits must add to the total and never repeat — the source of all killer-specific deductions.

Question 22

45 Rule

Accepted Answer

A Killer Sudoku tactic: since every row, column and box sums to 45, adding the cages in a region reveals a single leftover cell (an innie) or protruding cell (an outie).

Question 23

Region

Accepted Answer

The nine-cell group that replaces the 3×3 box in Jigsaw Sudoku. It can be any connected shape, but like a box it must still contain 1–9 once.

Question 24

Diagonal

Accepted Answer

In Sudoku X, each of the two main diagonals is an extra unit that must contain 1–9 once. The centre cell lies on both.

Question 25

Scanning

Accepted Answer

Searching a unit or the whole grid for forced placements — usually for hidden singles by digit — before resorting to pencil marks or advanced techniques.

Question 26

Elimination

Accepted Answer

Removing a candidate from a cell because the logic rules it out. Most techniques beyond singles work by elimination, narrowing cells until a single remains.

Question 27

Cell

Accepted Answer

One of the 81 squares of a classic grid (16 in a 4×4, 36 in a 6×6). Each cell holds exactly one digit in the finished puzzle.

Question 28

Row

Accepted Answer

A horizontal line of cells running across the grid. Each row must contain every digit exactly once — nine cells, 1–9, in classic Sudoku.

Question 29

Column

Accepted Answer

A vertical line of cells running down the grid. Like a row, each column must contain every digit exactly once.

Question 30

Grid

Accepted Answer

The whole playing board: 9×9 cells split into nine boxes for classic Sudoku, 6×6 for mini, or 4×4 for kids.

Question 31

Peer

Accepted Answer

A cell that shares a row, column or box with a given cell, so the two can never hold the same digit. Each cell in a classic grid has 20 peers.

Question 32

Band

Accepted Answer

A horizontal group of three boxes — three stacked rows of boxes across the grid. A classic grid has three bands.

Question 33

Stack

Accepted Answer

A vertical group of three boxes running down the grid. A classic grid has three stacks; together with the bands they frame box-based deductions.

Question 34

Chute

Accepted Answer

A band or a stack — any line of three boxes. A classic grid has six chutes: three bands and three stacks.

Question 35

Single

Accepted Answer

A cell or unit where a digit has only one possible home. Naked singles (one candidate in a cell) and hidden singles (one cell for a digit in a unit) are the bread and butter of solving.

Question 36

Naked Pair

Accepted Answer

Two cells in one unit that hold only the same two candidates. Those two digits are locked to those cells, so they can be erased from the rest of the unit.

Question 37

Hidden Pair

Accepted Answer

Two digits that can go in only the same two cells of a unit. Every other candidate can be cleared from those two cells, even though they hold other notes.

Question 38

Pointing Pair

Accepted Answer

When a digit in a box is confined to one row or column, it "points" along that line, so the digit can be removed from the rest of the line outside the box.

Question 39

Claiming (Box/Line Reduction)

Accepted Answer

When a digit in a row or column appears only inside one box, the line "claims" it, so the digit can be removed from the rest of that box.

Question 40

X-Wing

Accepted Answer

A single-digit pattern over two rows and two columns: the digit is confined to the same two columns in two rows, forming a rectangle that clears those columns elsewhere.

Question 41

Swordfish

Accepted Answer

A three-line fish — the X-Wing pattern stretched across three rows and three columns for one digit.

Question 42

Jellyfish

Accepted Answer

A four-line fish: the same single-digit fish logic over four rows and four columns.

Question 43

XY-Wing

Accepted Answer

Three bi-value cells forming a hinge (pivot) and two pincers. Whichever value the pivot takes, a shared digit is forced into one pincer, eliminating it from cells both pincers see.

Question 44

Skyscraper

Accepted Answer

A single-digit chain pattern: two conjugate pairs that share one line but whose other ends are mis-aligned, so cells seeing both far ends lose the digit.

Question 45

Weak Link

Accepted Answer

A relationship where two candidates cannot both be true (though both could be false). Weak links alternate with strong links to build chains.

Question 46

Bilocation

Accepted Answer

A unit in which a digit has exactly two candidate cells. The two locations form a strong link — the basis of fish, colouring and many chains.

Question 47

Almost Locked Set (ALS)

Accepted Answer

A group of N cells in one unit sharing N+1 candidates — one digit short of being locked. ALS logic powers several advanced elimination techniques.

Question 48

Fin

Accepted Answer

An extra candidate that spoils an otherwise clean fish. A finned fish still allows eliminations in the cells that can see the fin.

Question 49

Sashimi

Accepted Answer

A finned fish whose core pattern would fall apart without the fin. The eliminations still hold for cells that see the fin.

Question 50

Nishio

Accepted Answer

A what-if test: tentatively place a candidate, follow its forced consequences, and if they break the puzzle, eliminate that candidate.

Question 51

Brute Force

Accepted Answer

Solving by trying values and backtracking on contradictions rather than by logic. Computers use it; human solvers avoid it in favour of deductions.

Question 52

Backtracking

Accepted Answer

The trial-and-error method behind brute force: guess a digit, advance, and rewind to the last guess whenever a contradiction appears.

Question 53

Proper Puzzle

Accepted Answer

A puzzle with exactly one solution. Every well-made Sudoku is proper, which is what lets uniqueness techniques work.

Question 54

Minimal Puzzle

Accepted Answer

A proper puzzle from which no given can be removed without creating a second solution. A classic Sudoku needs at least 17 givens to stay proper.

Question 55

Symmetry

Accepted Answer

A balanced arrangement of givens — often rotationally symmetric — used by puzzle makers for visual appeal. It is an aesthetic choice, not a solving rule.

Question 56

Snyder Notation

Accepted Answer

A sparse pencil-marking method: mark a digit in a box only when it has exactly two possible cells there, keeping the grid readable while exposing pairs.

Question 57

Wing

Accepted Answer

A small family of bi-value patterns — XY-Wing, XYZ-Wing and W-Wing — where a pivot forces a shared digit into a pincer, enabling an elimination.

Question 58

Colouring

Accepted Answer

Tracing a single digit through its strong links with two alternating colours; a cell seeing both colours, or a colour seeing itself twice, reveals an elimination.

Sudoku Glossary

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