What does it mean?
Gain before a nonlinear stage can change saturation and timbre. Gain after it may mainly change level. A knob's position is not a gain value in dB unless its mapping explicitly says so.
ExampleA boost before an amp can add drive; after the amp, it may mainly raise output level.
How the meaning changes between controls
Amplifier
Native Gain drives the amp's nonlinear stage. For NAM, Input trim adjusts level before the capture.
Equalizer
Band gain changes a selected frequency region, rather than raising the entire signal evenly.