"Pointing pairs" technique.

"Pointing pairs" applies when a Note is present twice in a block and this Note also belongs to the same row or column. This means that the Note must be the solution for one of the two cells in the block. So, you can eliminate this Note from any other cells in the row or column.

To understand "Pointing pairs" better, let's take a look at the example.

Let's look at the block at the top left corner. All the cells that might contain number 4 are located in one column. As number 4 should appear in this block at least once, one of the highlighted cells will surely contain 4.

Hence, we can safely eliminate all other possible 4s from all the cells of this column.

Remember that you can do the same trick for blocks, rows, and columns.

That's it for "Pointing pairs" technique. Now you can proceed with the following Sudoku strategy "Pointing triples".