Geogrid typically has woven strands of fibers in two directions; transverse and longitudinal (or in the roll direction or sometimes called the machine direction). Geogrid rolls are typically manufactured in 6 or 12 ft wide rolls and have as much as 250 ft on each roll. Lightweight geogrids are very commonly Bi-Axial, meaning that their transverse and longitudinal strands are the same strength and these grids are more common in residential applications. Commercial strength geogrids are Uni-Axial meaning their longitudinal strands are stronger than the transverse strands. Using these Uni-Axial geogrids in a retaining wall means that you must roll the grid layers out perpendicular to the wall so the strong members are running perpendicular to the wall providing the most shear strength to the wall structure.
The weaker transverse strands play a very important role in the grids function as well. They are woven to the longitudinal strands to keep them aligned and they add lateral soil pullout resistance when embedded in the soil mass.