olemus
väljundväärtuse ja sisendväärtuse suhe

Merriam-Webster, noun:
3b: the increase (as of voltage or signal intensity) caused by an amplifier
especially : the ratio of output over input
3c: the signal-gathering ability of an antenna

näiteid
elektroonikas:
https://en.wikipedia.org/wiki/Gain_(electronics)
antennitehnikas:
https://en.wikipedia.org/wiki/Antenna_gain
laserifüüsikas:
https://en.wikipedia.org/wiki/Gain_(laser)
juhtimisteoorias:
https://en.wikibooks.org/wiki/Control_Systems/Gain