Dynamic processing (gate/compressor) which reduces the volume of a signal when the trigger signal exceeds a specified level.
Often shown as a gate option.
A normal gate is shown on the graph as a triangle truncated on the left, so very low volumes produce zero output, then normal behaviour is resumed above that level.
A ducking gate is truncated on the right, very high levels get turned off.
One use we make at church is to have the vocal FX channel ducked by the “vocal boost” mix, which boosts the vocalists signal to the loop and foyer mixes for when they start speaking (as opposed to singing).