Naked Triplet
A Naked Triplet turns up when three cells in the same house — a row, column, or 3×3 box — together hold only three distinct candidate digits between them. Those three digits have to fill those three cells, so every other cell in the house can have all three crossed off its pencil marks.
What is a Naked Triplet?
A Naked Triplet is the three-cell version of a Naked Pair, and it comes in more than one shape. The three cells don't each need the same three candidates — what matters is that across all three cells, only three distinct digits appear. So one cell might have {2, 6}, another {6, 7}, and the third {2, 7}: between them that's still just 2, 6 and 7. Whatever the split, those three digits are locked into those three cells, and the rest of the house is cleared of them. It's harder to eyeball than a pair because the candidates are spread across three cells instead of two, but the logic is identical.
How to spot it
Scan each house for three cells whose combined candidates total three digits or fewer. With pencil marks on, look for clusters of cells that draw from a small shared pool — if three cells only mention three digits between them, that's your triplet. The candidates don't have to match cell-for-cell, which is what trips people up: the test is on the union of candidates, not on each cell individually. Naked Triplets show up most often in harder puzzles once the pairs and singles have thinned the field.
The logic
Every house places each digit 1–9 exactly once. If three cells in a house between them can only hold three specific digits, those three digits must be distributed across those three cells — one digit per cell — because there's nowhere else in the house any of them can land. That uses up all three digits inside the triplet, so no other cell in the house can contain any of them. The same reasoning with four cells and four digits gives a Naked Quad, and with two it's the Naked Pair you already know.