Sudoku Variant Glossary: Cages, Thermos, Whispers, and More

Why you need a sudoku variant glossary

Classic Sudoku has one rule to learn, but the wider world of variants has grown a rich language of its own. Open a modern puzzle and you may meet cages, thermos, and whisper lines within the first minute, and without a sudoku variant glossary the clues can look like a foreign alphabet. The good news is that almost every variant simply adds one extra constraint on top of the familiar grid. Learn the vocabulary once, and a whole library of inventive puzzles suddenly opens up to you.

The foundation stays the same

Before the fancy terms, remember what never changes. In nearly every variant, the base rule of classic Sudoku still applies: each row, column, and box holds the digits one through nine exactly once. Everything in this sudoku variant glossary is an addition layered on that foundation, not a replacement for it. Keeping this in mind makes variants far less intimidating, because you are never learning a brand new game. You are learning one extra rule at a time, and the reliable classic logic keeps working underneath the whole time.

Common cage and region terms

• Cage, a dotted-line region whose cells must sum to a small printed total, usually with no repeats inside it.
• Killer sudoku, the popular style built entirely from these summed cages instead of given digits.
• Region, any group of cells that shares a constraint, whether a box, a cage, or a custom shape.
• Jigsaw or irregular, where the nine regions are odd shapes rather than neat three-by-three boxes.

Line-based constraints

Many modern puzzles hang their rules on lines drawn across the grid, and this part of a sudoku variant glossary is where a lot of the fun lives. A thermo, short for thermometer, is a line with a rounded bulb where the digits must increase as they travel away from the bulb. A whisper line, often called a German whisper, requires that neighboring digits along it differ by at least five. A renban line asks for a set of consecutive digits in any order. Each line type adds a distinct flavor of deduction to the solve.

Dots, arrows, and other markers

1. Arrow, where the digits along the arrow must sum to the digit sitting in its circle.
2. Kropki dots, small marks between cells showing a difference of one or a ratio of two.
3. XV clues, where an X means two cells sum to ten and a V means they sum to five.
4. Palindrome line, where the sequence of digits reads the same forwards and backwards.

From glossary to confident solving

With these terms in hand, a page that once looked baffling becomes an invitation. The trick is to start simple: master classic grids until the base logic is second nature, then add one variant at a time so each new rule in the sudoku variant glossary has room to sink in. A strong grasp of the fundamentals makes every variant easier, since you always fall back on the same reliable scanning and elimination. Shapedoku is a gentle place to build that base, keeping the classic rules while trading digits for nine glowing shapes, and its guided tutorial on shapedoku.com welcomes newcomers before they ever tackle a cage or a thermo.