Naked Triple

Three cells in a unit form a naked triple when, between them, they only ever contain three candidate digits in total — even if no single cell lists all three.

Those three digits must fill exactly those three cells, so they can be eliminated from every other cell in the unit.

Three cells in a column might show candidates {1, 4}, {4, 7}, and {1, 7} — no single cell lists all three digits, but across all three cells only 1, 4, and 7 ever appear. That's still a naked triple: those digits must fill those three cells in some order, so they can all be eliminated elsewhere in the column.