- Almost Locked Set (ALS) – A set of N unsolved cells with N+1 candidates
- Bi-location – A unit with only two occurances of a candidate X
- Bi-value – A cell with only two candidates remaining
- Box – Any 3x3 shaped unit in a normal sudoku, or any squiggly 9-cell shape in Jigsaw sudoku which must contain 1 to 9. There are 9 boxes in 9x9 sudoku.
- Cage – A marked off group of cells for which their sum is provided in Killer Sudoku and variants.
- Candidate – A possible solution for a cell. Any cell reduced to one candidate is solved.
- Cell – A square on the sudoku grid for which there is one single number solution.
- Chain – A sequence of links between candidates such that the two ends imply an elimination. All Loops are closed chains.
- Conjugate Pair – The two remaining candidates in a bi-location are conjugate. They are used to form strong link within a unit since one must be true and the other must be false.
- Contradiction – In Sudoku an illegal and therefore contradictory situation can occur if a) there are no candidates left in a cell, or b) two or more cells claim to be true. The aim of many strategies is to show a contradiction.
- Continuous – In a Loop it signifies that the links between nodes strictly alternate between strong and weak links.
- Cycle – Another name for a Loop. See Loop.
- Discontinuous – In a Loop it signifies that there is one discontinuity where a node is beset by either two weak links or two strong links.
- Grouped Node – A set of candidates of the same value (that must share a unit) that can be used to form a group with the effect of being able to treat it as a single cell.
- Hinge – In a Y-Wing the middle cell which joins the two pincer cells.
- Inference – Valid deductions that can be made between two linked candidates. There are inferences of the weak kind and the strong kind.
- Locked Set – A group of N candidates confined to a group of N cells. All candidates that can see a locked set can be removed. Naked Pairs, Triples etc are Locked Sets.
- Loop – Another name for a Cycle. See Cycle. A closed chain or sequence of candidates (which are called nodes in the loop) used to make a deduction. Loops are continuous or discontinuous.
- Pincer – In a Y-Wing or Y-Wing Chain the two end nodes are pincers which attack a cell for the purposes of elimination. See also Hinge.
- Strong Inference – Where two candidates X and Y are linked with strong inference then both cannot be false at the same time. Therefore if X is false Y is true and if Y is false X is true.
- Strong Link – A link between two candidates (which can be a single number or a grouped node) whereby if one is deemed false the other must be true. Strong Links can be between two cells (bi-location), within a call (bi-value) or as part of an ALS or more complex structure. Article here
- Unit – My preferred term for any row, column or box. Also called a house.
- Variant – A variation on an original puzzle, eg Jigsaw Sudoku is a variant of Sudoku.
- Weak Inference – Where two candidates X and Y are linked weak inference implies that both cannot be true at the same time. Therefore if X is true Y is false and if Y is true X is false.
- Weak Link – A link between one candidate and all others in a unit or cell whereby if the candidate is deemed to be true all the others are false. A strong link can be deemed to be weak merely because "all the others" includes cases where there is only one other. Article here
- XY-Wing – Another name for Y-Wing

**Block**– Another name for a box**Chute**– Three boxes in a column.**Domain**– Another term for a unit.**Given**– Another name for a clue.**House**– Another name for a unit, sometimes also the same as a chute.**Reduction**– Another name for elimination**Region**– Another name for a box

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