It's where you make a 9 patch then slice it through the center from top to bottom and side to side. Take top left corner and bottom right corner and turn them around so that the small square is on the outside corner. I know a lot of people here like them but I think they're a pain in the posterior. It's much easier to take a 4 1/2" strip, sew a coordinating 2 1/2" strip to it and cut it into 4 1/2"x 6 1/2" pieces. Take another 4 1/2" strip the same color as the narrow strip on the first piece and sew it to a 2 1/2" strip of another coordinating color. Cut them into 6 1/2"x 2 1/2" pieces and sew one onto the first piece with the square pieces in opposite corners. Make them in sets of 4, sew them together with the small square outside on opposite corners. It's the exact same thing as the D9P but so much easier and faster.