Naked Triple
A Naked Triple — also written Naked Triplet — is three cells in one row, column, or box whose combined candidate set contains exactly three digits. Those cells reserve the three digits, allowing the digits to be removed from other cells in the house.
What is a Naked Triplet?
Take the union of the candidates in three selected cells. It must contain exactly three distinct digits; the individual cells can contain two or three of them and need not have identical notes.
Walkthrough example
A walkthrough of one Naked Triple: three cells whose three-candidate union locks all three digits inside one house.
Step 1
Consider this block.
Step 2
The highlighted cells inside it can only contain values 2, 6 and 7.
Step 3
This means that these cells will definitely contain 2, 6 and 7 in some order, so we can remove these notes from all other cells in this block.
Three cells with a three-digit candidate union consume all three digits between them — that confinement is what justifies removing those digits from every other cell in the same house. You can start a free Sudoku game to practise spotting it on real puzzles.
How to spot it
Find three cells in one house whose candidate union has size three. Then check the other cells in that house for those digits.
The logic
Three cells require three different values and can draw only from a three-digit union. They occupy all three digits between them, so those digits can be removed from every other cell in the house.