Naked Pair

If any two cells in a row, Column or 3x3 box has the same 2 possible candidates then those two numbers can be eliminited from the buddy cells of both those cells. The example below will make it clear.

In Row1, R1C2 has the possibilities of 5,9 and also R1C8 has the possibility of 5 and 9 again. Hence irrespective of where the 5 and 9 come in these 2 cells, they cannot occur in any cel which is a buddy to both these cells. Cell R1C9 is a buddy to R1C2 and also to R1C8 hence neither 5 nor 9 can be in R1C9. Similarly, if we look at Box 2, R2C5 and R3C5 both have possibilities of 3 and 4 so irrespective of that neither number can be in R3C6 which is a buddy to R3C5 and R2C5.

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