Sudoku Glossary — Every Term from Naked Single to Swordfish

Cubedoku Guides · Published 2026-06-11

Sudoku has a vocabulary problem: guides casually say things like “the pointing pair eliminates the candidate” and lose half their readers. This page defines every term you will meet in our guides and around the wider Sudoku world, grouped so related ideas sit together. Bookmark it; nobody memorises these in one pass.

The board

Cell — one square of the grid, holding exactly one digit in the finished puzzle.
Row / Column — a horizontal / vertical line of cells. Each must contain every digit exactly once.
Box (also region or block) — the bold-bordered sub-grid (3×3 on a classic 9×9). The third unit type alongside rows and columns.
Unit (or house) — any row, column or box; the scope inside which digits cannot repeat.
Given (or clue) — a digit printed in the starting position. The rest are yours.
Latin square — the underlying mathematical object: a grid where each symbol appears once per row and column. Sudoku is a Latin square with the box constraint added; Skyscraper is one with visibility clues instead.
Unique solution — the contract of every well-made puzzle: exactly one valid completion exists, reachable by logic with no guessing. Every Cubedoku board is generated and verified to keep this promise.

Candidates and notes

Candidate — a digit not yet ruled out for a cell.
Pencil marks (or notes) — small digits recording a cell's remaining candidates. Used sparingly by strong solvers (see beginner habits).
Elimination — striking a candidate from a cell because some deduction forbids it. Advanced techniques are essentially industrial-scale elimination.

Singles — the basic placements

Naked single— a cell with exactly one candidate left. Answers “what can this cell be?”
Hidden single— a digit with exactly one legal cell left inside some unit. Answers “where can this digit go?” — the workhorse of fast solving.
Full house — the last empty cell of a unit; the friendliest move in Sudoku.
Cross-hatching (or scanning) — sweeping one digit across the grid, striking out rows and columns that already contain it, to expose hidden singles.

Subsets — the intermediate tier

Naked pair / triple — two (three) cells in a unit whose candidates are limited to the same two (three) digits; those digits can be eliminated from the rest of the unit.
Hidden pair / triple — the mirror image: two (three) digits restricted to the same two (three) cells, so everything else in those cells can be erased.
Pointing pair— all of a box's candidates for some digit sit in one row or column, so the digit is excluded from that line outside the box.
Box-line reduction (or claiming) — the reverse: a line's candidates for a digit all fall in one box, clearing the rest of that box. Both are unpacked in the intermediate guide.

Fish and wings — the advanced tier

X-Wing — one digit confined to the same two columns in each of two rows (or vice versa), forming a rectangle that eliminates the digit elsewhere in those columns.
Swordfish — the 3×3 generalisation of the X-Wing, across three rows and three columns.
Jellyfish — the 4×4 member of the same family. Rare in practice; satisfying in theory.
XY-Wing — three two-candidate cells linked in a pivot-and-pincers shape; whichever way the pivot resolves, both pincers cannot avoid eliminating a shared candidate. Step-by-step in the advanced guide.

Killer Sudoku terms

Cage — a dotted-line group of cells whose digits must sum to the printed total, with no digit repeating inside the cage.
Rule of 45 — every row, column and box of a 9×9 sums to 45; comparing cage totals against 45 yields values for cells that poke in or out.
Innie / outie — the cell of a cage that pokes into (out of) a region whose other cells are fully covered by cages; the 45-arithmetic pins its exact value.
Forced cage — a cage whose sum admits exactly one digit combination (a 2-cell 17 is always 8+9). The complete list lives in the cage combination cheat sheet.

Cubedoku-specific terms

The Cube — our 3D mode: Sudoku wrapped around all six faces of a rotating cube, with shared edges linking the faces' constraints.
Sub-cube — in Avalanche, one of the 3³ blocks a large cube is split into; completing one collapses it.
Clue decay — the Blitz mechanic: a starting clue disappears every few seconds, and placing a digit resets the countdown.
Daily Challenge — one shared puzzle for the whole world each day, with a worldwide leaderboard; the backbone of a daily habit.
Streak — consecutive days with the Daily completed. Motivation, gamified honestly.

Difficulty words you will hear

Technique-graded — difficulty measured by the hardest technique a puzzle requires, not how empty it looks — the grading philosophy explained in choosing the right difficulty.
Bifurcation — solving by trying a guess and following consequences until contradiction. Works, teaches nothing; well-made puzzles never require it.
Cognitive reserve— the buffer of mental capacity built by lifelong engagement; the concept behind the honest version of “puzzles keep you sharp”, examined in our look at the dementia evidence.

Missing a term you ran into elsewhere? Tell us at support@cubedoku.com and we will add it — this page is maintained by hand, like everything in the guides.

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