Hidden PairA Hidden Pair occurs when two digits are candidates only in two cells of a house. Other candidating digits can be eliminated from these cells.
In the sudoku diagram below, the digits 2 and 6 can only be entered in the R2C1 and R2C3 cells in the upper left box. The remaining digits 3, 7 and 9 can be eliminated from these cells. Thanks to this elimination, in the third column, the digit 9 can only be placed in the R6C3 cell..