Reverb is a post-effect. It takes incoming audio and adds synthetic echoes or sound reflections, giving it the sound of being played in a large room. It does this by using filters to feed the sound back into itself.
The effect can range from a very short stereo reflection, to a cavernous long dense tail.
In the Reverb’s options, ‘Room Size’ sets the amount of the effect – how long the tail is and how much of the sound is fed back on itself. ‘Dampening’ sets how “lively” it sounds, allowing the reflections to sound muted, with the treble reduced, or with the treble left in-tact making a more prominent reverb. ‘Mix’ blends between the original signal and the reverberated audio.