—n. 1. a break or opening, as in a fence, wall, or military line; breach: We found a gap in the enemy's line of fortifications. 2. an empty space or interval; interruption in continuity; hiatus: a momentary gap in a siren's wailing; a gap in his memory. 3. a wide divergence or difference; disparity: the gap between expenses and income; the gap between ideals and actions. 4. a difference or disparity in attitudes, perceptions, character, or development, or a lack of confidence or understanding, perceived as creating a problem: the technology gap; a communications gap. 5. a deep, sloping ravine or cleft through a mountain ridge.
6. Chiefly Midland and Southern U.S.a mountain pass: the Cumberland Gap. 7. Aeron.the distance between one supporting surface of an airplane and another above or below it.