Glossary of Sudoku
A Sudoku puzzle (image hyperlinked to solution)
This is a glossary of Sudoku terms and jargon.

List organization and conventions
This list provides a brief glossary of Sudoku terminology. Items are listed thematically, and usually only once, with a brief description and possibly a link to a detailed description. Links to example usage are provided as inline numbered references (like [1]). Here the default usage of Sudoku refers to the prominent 9x9 format, as illustrated.
Grid layout and puzzle terms
A Sudoku grid has 9 rows, columns and boxes each having 9 cells. The full grid has 81 cells. Cells are commonly called squares, but in technical descriptions the term square is avoided since the boxes and grid are also squares. Boxes are also known as blocks or zones. Three vertically stacked blocks make a stack. Three horizontally connected blocks make a band. A chute is either a band or a stack. A grid has three bands, three stacks and six chutes.
The use of the boxes to partition the grid can be generalized to other equalsized partition shapes, in which case the subareas are known as regions, zones, subgrids, or nonets. See Variants below. In some cases the regions are only equal sized, not equal shaped.
Rows, columns and regions are collectively referred to as units or scopes, of which the grid has 27. The One Rule can then be compactly stated as: "Each digit appears once in each unit".
Size refers to the size of a puzzle or grid. Often a composite row x column designation is used, e.g. size 9x9. In technical discussions size may mean the number of cells, e.g. 81. Since the number of cells in a region must be the side dimension of the square grid, e.g. nine cells per block for a 9x9 grid, it is convenient to just use the region size, e.g. 9.
Puzzle terms
A puzzle is a partially completed grid. The initially defined values are known as givens or clues. A proper puzzle has a single (unique) solution. A proper puzzle that can be solved without trial and error (guessing) is known as a satisfactory puzzle. An irreducible puzzle (a.k.a. minimum puzzle) is a proper puzzle from which no givens can be removed leaving it a proper puzzle (with a single solution). It is possible to construct minimum puzzles with different numbers of givens. The minimum number of givens refers to the minimum over all proper puzzles and identifies a subset of minimum puzzles. See Mathematics of Sudoku  Minimum number of givens for values and details.
Sudoku variants
The classic 9x9 Sudoku format can be generalized to an
 NxN rowcolumn grid partitioned into N regions, where each of the N rows, columns and regions have N cells and each of the N digits occur once in each row, column or region.
This accommodates variants by region size and shape, e.g. 6cell rectangular regions (The NxN Sudoku grid is always square). For prime N, polyominoshaped regions can be used. The requirement to use equal sized regions, or have the regions cover the grid entirely can also be relaxed.
Other variation types include additional value placement constraints, alternate cell symbols (e.g. letters), alternate mechanism for expressing the clues, and composition with overlapping grids. This page provides a simple list of variants. See Sudoku  Variants for details and additional variants.
For rectangular regions the rowcolumn dimensions of the region may be used to describe the grid as whole, e.g. 3x2, since each of the grid side dimensions must be the product of rowxcolumn, e.g. for a 3x2 rectangular region, the grid must be 6x6. For rectangles of size Nx1 or 1xN, the region is a row or column, and Sudoku becomes a Latin square.
Sudoku types and classes
 Sub Doku
 Grids smaller than 9x9. Sometimes referred to as "Children's Sudoku" (especially the 4x4 variant) as the reduced number of possibilities makes them easier to solve.
 Super Doku
 Grids larger than 9x9.
 Prime Doku
 NxN grid where N is prime. Generally constructed with polyomino regions, e.g. Go Doku and pentominos.
 Maximum Su Doku
 The class of puzzles which have the maximum number of independent clues needed to allow a complete and unique solution.
 Minimum Su Doku
 The class of puzzles which have the minimum number of clues needed to allow a complete and unique solution.
 Proper puzzle
 A puzzle that has a unique solution.
 Satisfactory puzzle
 A puzzle that does not require trial and error. Note: the level of trial and error is usually not explicitly defined, see trial and error below.
 Jigsaw Sudoku
 regular 9x9 Sudoku that row and column rules apply, but instead of a 3x3 grid they are nine Jigsaw shapes.
Variants by size
 Polyomino
 A shape composed of equal sized, sideadjacent squares. Often used for Sudoku region variants. Polyominos are named by size: (5) pentomino, (6) hexomino, (7) heptomino, (8) octomino, and (9) nonomino.
 Dusumoh
 5x5, 6x6, 7x7, 8x8 or 9x9 grid with irregular, polyomino, shaped regions and minimal number of clues.
DuSumOh puzzles are also known as Latin Squares Puzzles (invented by Mark Thompson), Squiggly Sudoku, Jigsaw Sudoku, Irregular Sudoku, or Geometric Sudoku. These puzzles typically have anywhere from 5 to 9 rows. The number of rows is always equal to the number of columns. The regions are polyominos made of the same number of squares that are in any one row of the puzzle. The irregularity of the regions compensates for the relatively small number of givens.
4x4
 Shi Doku
 Four 2x2 regions. Shi is Japanese for 4.
5x5
 Go Doku
 5x5 grid with pentomino regions. Go is Japanese for 5.
 Logi5
 5x5 grid with pentomino regions
6x6
These use six 2x3 rectangular regions:
 Roku Doku
 (unnamed)
 featured at the World Puzzle Championship
 Sudoku X  with unique main diagonals
7x7
 (unnamed)
 7x7 grid with six heptomino regions and a disjoint region, featured at the World Puzzle Championship.
8x8
Super Sudoku X  Four 4x2 + four 2x4 rectangular blocks.
9x9
 Sudoku
 Classic 9x9 grid with nine 3x3 regions.
 Jigsaw Sudoku
 9x9 grid with nonomino regions.
 Dusumoh
 5x5, 6x6, 7x7, 8x8 or 9x9 grid with irregular, polyomino, shaped regions and minimal number of clues.
Only "One Rule" variant puzzles with simple givens are listed in this section. For variants with other clue mechanisms, see Constraint and clue variants.
12x12
 Maxi
 Twelve 3x4 rectangular blocks.
16x16
 Number Place Challenger
 Sixteen 4x4 regions.
25x25
A 25x25 Giant Sudoku puzzle (link to solution)
 Sudoku the Giant
 Twentyfive 5x5 regions.
100x100
 Sudokuzilla
 100 10x10 regions.
Constraint and clue variants
Puzzles with additional constraints on the placement of values including various forms of expressing the constraints (e.g. < > relations, sums, linked cells, etc.).
 Main diagonals unique
 the cell values along both main diagonals must be unique, see Sudoku X.
 Relative digit location
 digits use the same relative location within selected regions. The matching cells or regions are often colorcoded.
Mathematics of Sudoku has identified numerous additional constraints as analytic possibilities.
 Samunamupure (clue sums)
 Regions of various shapes and sizes. The usual constraints of no repeated value in any row, column or region apply. The clues are given as sums of values within regions (e.g. a 4cell region with sum 10 must consist of values 1,2,3,4 in some order).
Terms related to solving
The meanings of most of these terms can be extended to region shapes other than blocks. To simplify reading, definitions are given only in terms of blocks or boxes.
 Scanning
 The process of working through a puzzle to look for or eliminate values.
 Cross hatching
 Process of elimination that checks rows and columns intersecting a block for a given value to limit the possible locations in the block.
 Counting
 Process of stepping through the values for a row, column or block to see where they can or cannot be used.
 Box line reduction strategy
 A form of intersection removal in which candidates which must belong to a line can be ruled out as candidates in a block (or box) that intersects the line in question.
 Candidate
 Potential value for a cell.
 Contingency
 A condition limiting the location of a value.
 Chain
 A sequence of contingencies connected by alternative values.
 Higher circuits
 Related locations outside the immediate row, column and grid. The locations are related by value contingencies.
 Independent clues
 A set of clues that cannot be deduced from each other. Often depends on the order of choosing the clues for a given grid.
 Intersection removal
 When any one number occurs twice or three times in just one unit (or scope) then we can remove that number from the intersection of another unit. For example, if a certain number must occur on a certain line, then occurrences of that number found in a block that intersects this line can be ruled out as candidates. Sometimes called Pointing (or matched) Pairs (or twins)/Triples (triplets) as they point out a candidate that can be removed.
 Nishio
 Whatif method of elimination, where the use of a candidate that would make its other (necessary) placements impossible is eliminated.
 The One Rule
 Fill in all (blank) cells so that each row, column and box contains the values 19. Same as: fill in the grid so that each row, column and box contains the values 19 exactly once, without changing the clues.
 Single or singleton or lone number
 The only candidate in a cell.
 Hidden single
 A candidate that appears with others, but only once in a given row, column or box.
 Locked candidate
 A candidate limited to a row or column within a block.
 Naked pair
 Two cells in a row, column or block, which together contain only the same two candidates. These candidates can be excluded from other cells in the same row, column or block.
 Hidden pair
 Two candidates that appear only in two cells in a row, column or block. Other candidates in those two cells can be eliminated.
 Trio
 Three cells in a unit sharing three numbers exclusively. See "Triples and quads".
 Triples and quads
 The concepts applied to pairs can also be applied to triples and quads.
 Xwing
 See Nfish (with N=2).
 Swordfish
 See Nfish (with N=3).
 Nfish
 Analogues of hidden pairs/triples/quads for multiple rows and columns. A pattern formed by all candidate cells for some digit in N rows (or columns), that spans only N columns (rows). All other candidates for that digit in those columns (rows) can then be excluded. Names for various Nfish:
 2fish: Xwing
 3fish: Swordfish
 4fish: Jellyfish
 5fish: Squirmbag  For 9x9 Sudoku, there's no in point naming higherorder (>4) fish, since every Nfish comes paired with a 9−N fish whose effect is the same (thus any 5fish is paired with a jellyfish; any 6fish with a swordfish; any 7fish with an xwing; any 8fish with a hidden or naked single). Nevertheless, a 5fish is occasionally called a squirmbag.
 6+ fish: 6gronk, 7gronk ...  these patterns are only useful for Sudoku larger than 9x9.
 Remote Pairs
 When a long string of naked pairs that leads around the grid exists, any cells that are in the intersection of the cells at the beginning and the end of the string may not be either of the numbers in the naked pairs, for example, 4 and 7.
Cell reference schemes
 1...81 or 0...80
 Row & column
 Box & cell
Math related terms
 Latin square  Related puzzle with only row and column constraints.
 Constraints  Rules or conditions. In Sudoku, the rule(s) requiring each digit appear once in each row, column and region.
 Triplet  The set of 3 values in a row or column within a block.
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