If a particular candidate is present in four or less Cells in four Rows and if these Cells belong to the same four Columns, then whichever Cells the candidate is the solution for in any of these four Rows, these Cells must be in different columns. As there are only four possible columns, the candidate can not be the solution anywhere else in these Columns.

The reasoning is also applicable when you replace "Row" by "Column" and "Column" by "Row".

The candidate must not be present in all Cells of the 4x4 pattern, as long as all allowed combinations of the Candidate present in the pattern result in the Candidate being the solution in each Row and in each Column of the 4x4 pattern.

In the example the jellyfish is formed by the cells with candidates 4 colored in green, plus J7. In the solution each row of the jellyfish must contain a candidate 4 and it must be in a different column in each of these four rows. Hence in Column "1" candidate 4 must be the solution in either A1, or D1, or F1, or J1; so it can be deleted in all the other cells of that column. The same reasoning also applies to Columns "3", "5" and "7".

You can practice this strategy by installing the SudokuCoach application on your Android™ device.