Rapid variations in received signal levels, such as variations that may be caused by
atmospheric disturbances,
antenna movements in a high wind, or interaction with other signals.
In
radio propagation, a phenomenon in which nearly all radio signals that are usually reflected by
ionospheric layers in or above the E-region experience partial or complete
absorption.
In radio
transmission, rapidly changing signal levels, together with variable
multipath time delays, caused by
reflection and possible partial absorption of the signal by aircraft flying through the radio beam or common scatter volume.
The variation in the transmission characteristics of a loaded
telephone line caused by the action of telegraph direct currents on the
loading coils.
In recording and reproducing equipment, the deviation of
frequency caused by irregular mechanical motion, e.g., that of
capstan angular velocity in a tape transport mechanism, during operation.[1][2]