A narrow passage between two elevations is called a notch. Also a depression or dent, an opening or defile, a cut in the surface of anything. In landscape, especially, a mountain pass. This is the location in a mountain range where a geological formation is lower than the surrounding peaks, thus allowing passage. Notch can simply indicate an opening through rough terrain. Also a term in hybridization, where a notch is a slit made in the ground to receive the roots of a seedling tree, or an incision made in a twig to stimulate growth of a bud lower down on the twig. Notch is also used to denote an opening extending above water level in a surface placed across a stream, like a weir. Finally, notch can be used freely to mean any narrow opening, a break or breach. Dozens of mountainous locations in the United States are known simply as “The Notch.” For instance, as Isabella Bird writes in A Lady’s Life in the Rocky Mountains: “On arriving at the ‘Notch’ (a literal gate of rock), we found ourselves absolutely on the knife-like ridge or backbone of Longs Peak, only a few feet wide, covered with colossal boulders and fragments, and on the other side shelving in one precipitous, snow-patched sweep of three thousand feet to a picturesque hollow, containing a lake of pure green water.”

Patricia Hampl