An air mass is a large body of air that has maintained relatively uniform temperature and moisture characteristics as it moves across the Earth's surface. These masses derive their properties from the climate of their source region, which dictates whether the air is dry, moist, warm, or cold. The interactions between different air masses—such as the collision of a cold, dense mass with a warm, buoyant mass—are fundamental drivers of weather systems, creating gradients in temperature and pressure. Understanding the movement and characteristics of air masses allows for the prediction of atmospheric stability, frontal boundaries, and general weather patterns across large geographical areas.