The phrase "perpendicular direction" means moving or pointing at a right angle to something else. It is like drawing a line or moving in a direction that forms a 90-degree angle with another line or direction. Full definition
To make the liquid crystal molecules in each cell stack up in the staircase - like fashion, displaymakers rub the two plastic layers that sandwich them in perpendicular directions with a velvet roller. (sciencemag.org)
It is then cut with a grooved rolling pin in perpendicular directions, cutting a grid into the dough which prevents it from creating air pockets as it cooks. (en.wikipedia.org)
Fold the dough into thirds again, and roll in a perpendicular direction to your first fold. (thefoodielovers.com)