"idle-channel noise: Noise that is present in a communications channel when no signals are applied. Note: The channel conditions and terminations must be stated for idle-channel noise measurements to be meaningful". ILI
"Idle channel noise, in dB, is a ratio of the full scale RMS signal
level to the RMS sum of all other spectral components
over the specified bandwidth using a zero amplitude signal.
ICN is a measure of the static noise produced by the device
with a zero amplitude signal. It is useful to have good ICN
performance in order to avoid an irritating noise commonly
referred to as hiss, random noise, or white noise. Leakage
from local sources, such as power lines, will show up and
degrade ICN performance as well...."

Po ovim i sličnim definicijama, mislim da bi to trebao biti šum kanala bez prisustva spoljašnje pobude/u pasivnom modu.