A term used to refer to the multiple paths taken by a signal from a radio transmitter to a fixed or moving receiver. These are the result of scattering from objects in the environment between the transmitter and receiver; the objects themselves may be fixed, such as hills or buildings, or moving, such as vehicles. The signals may add or cancel at the receiver leading to variations of up to several orders of magnitude in the received signal over very short distances. If the receiver is moving this leads to fading of the received signal.