Wind shear refers to the change in wind speed or direction over a short distance in the atmosphere. It can occur at any altitude and is often associated with weather phenomena like thunderstorms or the boundaries between different air masses. Pilots must be aware of wind shear, as it can affect aircraft performance during takeoff and landing. Wind shear can be vertical or horizontal. Vertical wind shear occurs when wind speed or direction changes with altitude, while horizontal wind shear happens when winds shift direction or speed across a horizontal plane. Understanding wind shear is crucial for safe aviation operations and weather forecasting.