Naked Pair
Two cells in the same row, column or box hold the same two candidates, so those two digits are used up between them.
How it works on this board
7 and 9 must be used within the highlighted cells
5
3
1
2
3
5
1
4
2
8
8
4
2
5
6
6
1
4
3
4
6
9
8
8
6
2
2
3
5
8
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