Mirrored from Sudopedia, the Free Sudoku Reference Guide
A part of the grid where 2 houses share one or more cells. Mostly used for intersections between a box and a row or column.
In standard Sudoku, there are 27 box-row intersections and 27 box-column intersections, each containing 3 cells.
Several Sudoku Variations have additional intersections between the extra houses and the lines and boxes.