What is defined as a column of air that moves upwards?

A column of air that moves upwards is referred to as a thermal. Thermals are created when the sun heats the earth's surface, causing the air above to warm up and become less dense than the surrounding cooler air. This causes the warm air to rise, creating a vertical column. Thermals are essential for various aerial activities, including gliding and soaring, as they provide lift for aircraft.

Draft, on the other hand, typically refers to a downward air movement or the movement of air inside a building. Current is often associated with larger-scale movements of air within the atmosphere, like a jet stream, and can include both upward and downward motions. Wind describes the horizontal movement of air from one location to another, rather than vertical ascent. Therefore, the specific upward motion of air that defines a thermal distinguishes it from the other choices.