Cross modulation is a form of intermodulation.
If you have ever been listening to a distant FM station while driving by an AM Broadcast station's transmitting tower; you more than likely heard both stations--one on top of the other. That effect was "Cross Modulation," a form of Intermodulation.
Since an FM receiver can only receive--Demodulate--one station at a time (unlike AM which cannot separate interfering stations), that is, two stations on the same frequency, the receiver will only demodulate the stronger of the two .
In the scenario above, you heard both the distant FM station and the very close AM transmitter. The FM station's signal, as it was entering the receiver's "Front End," was being Modulated by the very strong AM signal. In effect, the receiver's RF Amplifier was acting as a Detector (rectifier) varying its bias point, which caused the amplifier's gain to change rapidly (at the AM transmitter modulation rate). This varying gain is effectively Modulating (Multiplying) the distant FM station's signal. By the time this "Mess" reaches the receiver's Demodulator it appears to the Discriminator as an FM signal having two audio messages superimposed one on the other.