Pointing Triple
If a candidate is present in only three Cells of a Square, then it must be the solution for one of these three cells. If these three cells belong to the same Row or Column, then this candidate can not be the solution in any other cell of the same Row or Column, respectively.
In the example above candidate 8 must be the solution in either A4, or B4, or C4 in Square "2". Hence it can not be the solution in any other cell of Column "4".
You can practice this strategy by installing the free SudokuCoach application on your Android™ device.
