Overmodulation is the condition that prevails in telecommunication when the instantaneous level of the modulating signal exceeds the value necessary to produce 100% modulation of the carrier. In layman's terms, the signal is going "off the scale".
Overmodulation results in spurious emissions by the modulated carrier, and distortion of the recovered modulating signal.
Overmodulation in the sense of this definition is almost always considered a fault condition. It is defined as the condition that prevails when the mean level of the modulating signal is such that peaks in the modulating signal exceed the value necessary to produce 100% modulation of the carrier. Overmodulation is sometimes considered permissible.
