Pointing Pair
When all candidates for a digit within a block lie in the same row or column, that digit can be eliminated from other blocks along that row or column.
A Pointing Pair occurs when all candidate cells for a specific digit within a block are aligned in the same row or column. This allows the elimination of that digit from cells in other blocks along the same row or column.
Logical Basis
The digit must appear somewhere within the block. If all its candidates are in the same row, then the digit is locked into that row within this block. Therefore, no cell in the same row belonging to other blocks can contain that digit.
Relationship to Box/Line Reduction
Pointing Pair eliminates in the "block to row/column" direction. Conversely, Box/Line Reduction eliminates in the "row/column to block" direction. The logical basis is the same - constraint intersection - but the scanning direction differs.