The act of locking a radio receiver onto a wanted signal in the presence of many other signals. Very much like hearing your name called in a busy railway station – your brain has learned to “lock on” to that sound even in a very noisy background. If we tell each radio receiver its “name” it can lock onto the transmitter calling its “name” even when there are dozens or hundreds of interfering signals. Correlation is also used in GPS and other satellite navigation systems, to “lock on” the receiver’s internal clock to the precisely-timed signals from GPS satellites. By knowing the timing of the signals, the receiver can determine its location.