When referring to ground characteristics, which term describes a method involving perpendicular fire as opposed to parallel?

The term that describes a method involving perpendicular fire, as opposed to parallel, is known as flanking. Flanking fire occurs when troops engage an enemy from the side or an angle that is not directly in front of them. This technique is effective because it can exploit weaknesses in an enemy's defenses and create confusion and disarray. By delivering fire at a perpendicular angle, forces can achieve greater lethality and effectiveness in combat, targeting the enemy's vulnerable flank.

Understanding the concept of flanking is key in military operations, as it enhances maneuverability and creates tactical advantages over the enemy. The other terms—defilade, grazing, and oblique—refer to different combat scenarios or firing techniques and do not specifically denote the method of engagement with perpendicular fire.