In telecommunications, the term fade margin (fading margin) has the following meanings:
A design allowance that provides for sufficient systemgain or sensitivity to accommodate expected fading, for the purpose of ensuring that the required quality of service is maintained.
The amount by which a received signal level may be reduced without causing system performance to fall below a specified threshold value. It is mainly used to describe a communication system such as satellite, for example a system like globalstar operates at 25-35 dB Fade margin.
Attila Hilt, "Availability and Fade Margin Calculations for 5G Microwave and Millimeter-Wave Anyhaul Links", Applied Sciences, 2019, 9(23), 5240; https://doi.org/10.3390/app9235240.,