Hidden Triple

Like a hidden pair but with three digits and three cells: if three digits only ever appear as candidates in the same three cells of a unit, those three cells must hold those three digits.

Any other candidates in those three cells can be eliminated, revealing a naked triple underneath.

Hidden triples are the hardest of the pair/triple family to spot by eye, since the confining pattern is spread across three cells and three digits at once rather than jumping out from one obviously-matching cell. Working through one digit at a time — where can each of the three still go — is the systematic way to find them.