insertion loss and gain.
A device, circuit, stage, inserted in a signal path can have gain, expressed like a positive number or loss expressed as a negative number.
An amplification stage inserted in a signal path with the gain of -say 4- will be an insertion gain, not an insertion loss.
An attenuator inserted in a signal path with attenuation of -say 10- will be an insertion loss of 10 with result of a tenth of the signal; or gain of minus 10.
Well it's like we have a income and expenses.
It's just makes sense to have the two instead of seeing expenses like "negative income".
Expenses have a negative sign built in just like loss has.
That way we can say the feed-line has a loss of 12dB instead of saying it has a negative gain of 12dB, it's just easier.
Use it if you like, it's up to you and it helps when you communicate with others. I guess other will think you are a bit nutty if you say the attenuator has a negative gain of 40dB, even if it is correct
a passive device is often talked about as having an insertion loss. Like the insertion loss of my filter is 3 dB. So the output power is half of the input power.
Active devices are often discussed as having a gain. Like my amplifier has 10 dB of gain. or the output power is 10 times the input power.
it is just a way of not getting confused with a +/- sign