Crosstalk - definition
A phenomenon by which a signal transmitted on one circuit or channel creates an undesired effect on another circuit. Generally rare in modern digital wireless phone systems but not entirely eliminated.
Stereo crosstalk for example is one of the parameters of audio quality we test when reviewing mobile phones. The crosstalk measurement is made to determine the amount of signal leaking across from one channel to another or - in purely non-technical terms - it measures how good the stereo is.