Define "severe turbulence".

Severe turbulence is characterized by its potential to induce drastic changes in an aircraft's altitude and/or attitude, making it a significant concern for pilots and crew. This type of turbulence can lead to abrupt movements that may result in difficulty controlling the aircraft, posing risks to safety. It often occurs in situations associated with strong atmospheric phenomena, such as thunderstorms or turbulent air currents at high altitudes.

In contrast, other forms of turbulence, such as those described in the other options, do not reach this level of impact. For instance, turbulence without noticeable effects or only causing minor altitude changes indicates a much less severe disruption, allowing for continued stable flight. Additionally, turbulence that is typical during takeoff and landing usually involves mild experiences that pilots are well-prepared to handle and does not reflect the intensity or danger associated with severe turbulence. Understanding this distinction helps pilots and flight crews to assess and respond appropriately to various turbulence conditions during flight.