Naked Pair

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

Naked Pair is a size-$2$ subset.

A naked pair can appear in a row. For example, in row $6$ below, cells $R6C6$ and $R6C7$ contain only candidates $2$ and $5$, so those candidates can be eliminated from the other cells in the row.

A naked pair can also appear in a column. For example, in column $6$ below, cells $R5C6$ and $R7C6$ contain only candidates $3$ and $8$, so those candidates can be eliminated from the other cells in the column.

A naked pair can also appear in a box. For example, in box $7$ below, cells $R7C3$ and $R9C1$ contain only candidates $1$ and $5$, so those candidates can be eliminated from the other cells in the box.