Multipath
The phenomenon of a radio device receiving the same signal multiple times, slightly offset in time.
This often happens when a radio signal is received directly from the transmitter, and also reflected off of one or more nearby objects, such as large buildings. Because a reflected signal takes a longer "path", it is slightly delayed compared to the direct signal.
Multipath is generally a type of interference; it is how a single signal can interfere with itself. Most types of radio signals are therefore degraded by multipath.
Some technologies, however - such as CDMA - are specifically designed to harness multipath effects. CDMA signals can actually benefit from multipath.
