Define "turbulence" in the context of flight and weather.

Turbulence, in the context of flight and weather, refers to the irregular or violent movement of air that can lead to sudden changes in an aircraft's altitude or speed. This phenomenon occurs due to various atmospheric conditions, such as thermal updrafts, wind shear, or the interaction of different air masses. When an aircraft encounters turbulence, the airflow around it becomes chaotic and unpredictable, causing the aircraft to experience unexpected jolts and shifts.

Unlike the other options, which describe stable or smooth air characteristics, the essence of turbulence lies in its unpredictability and the potential for significant impact on flight safety and comfort. This is particularly important for pilots to understand as it can affect both the operation of the aircraft and the welfare of the passengers.