In telecommunication, FM improvement threshold is the point in an FM (frequency modulation) receiver at which the peaks in the RF signal equal the peaks of the thermal noise generated in the receiver. A baseband signal-to-noise ratio of about 30dB is typical at the improvement threshold, and this ratio improves 1dB for each decibel of increase in the signal above the threshold.

Source: from Federal Standard 1037C and from MIL-STD-188