Strategy Detailed Descriptions Strategy Detailed Descriptions This is sometimes referred to as "Intersection Removal".
Often a number is only Possible in a single row or a single column of a box. When that occurs, then that number can be marked Impossible in all cells of that row or column outside the box. This is sometimes referred to as "Pointing Pairs/Triples".
Similarly, for a row or column, if a number is only Possible within one box, then it can be marked impossible in other rows or columns of that box. This is sometimes referred to as "Box Line Reduction".
In the example above, note that the only cells in the left box that can contain the number 6 are in the third row. Therefore the number 6 can be marked impossible in the remaining cells of the third row.
Also, note that the only cells in the first row that can contain the number 5 are in the third box. Therefore the number 5 can be marked impossible in the remaining cells of the third box.