Naked Triple

A naked triple occurs when, in a house (row, column, or box), three cells contain only three candidates, and those three candidates are confined to those three cells. In that case, those three candidates can be eliminated from every other cell in the house. No matter how the digits are arranged, they must occupy those three cells.

Naked Triple is a size-$3$ subset.

A naked triple can appear in a row. For example, in row $5$ below, cells $R5C1$, $R5C5$, and $R5C6$ contain only candidates $1$, $4$, and $8$, so those candidates can be eliminated from the other cells in the row.

A naked triple can also appear in a column. For example, in column $8$ below, cells $R2C8$, $R3C8$, and $R7C8$ contain only candidates $1$, $3$, and $9$, so those candidates can be eliminated from the other cells in the column.

A naked triple can also appear in a box. For example, in box $4$ below, cells $R4C3$, $R6C1$, and $R6C2$ contain only candidates $1$, $3$, and $4$, so those candidates can be eliminated from the other cells in the box.