Link margin is the system design concern to the communication link and does not concern the only feed system of communication link, fade margin is particularly concern with the feed system of communication link.

In an analog microwave radio system, the flat fade margin is equal to the system total Gains minus system total losses

In a digital microwave radio system, the "flat" or thermal fade margin (TFM) is calculated from the system total Gains minus system total losses.

When writing a film script, the first words in the script are fade-in, in all caps and positioned at the left margin.

Surrounded by a distinct margin. I.e it does not gradually fade away.

Thermal fade margin TFM in db is the difference between the normal received signal RSL at the input of microwave receiver expressed in dbm and the receiver's threshold ( given by the manufacturer) expressed in dbm TFM = RSL - TH