This is the reverse of pointing pairs. If, within a row or column, all possible locations that the number can appear are in the same jigsaw piece, the number can be eliminated from any other cells in that jigsaw piece.
Take this example:
The number 1 in the central column can only be within one jigsaw piece:
This means that it can only appear in one of the two cells in this column. It can be removed as a possibility from other cells in this jigsaw piece:
