Reverb is that shimmering effect you hear on vocals, that immense sound in a church or the gentle wash of atmosphere on your synth pads. It is the most overused effect out there but when used correctly, can make your sound beautiful.
Used well, then, a touch of reverb here or there can add a completely new dimension to your mix. Early reverbs simulated the effect mechanically using large plates. The larger the plate, the longer the reverb time. Reverb chambers is simply capturing the sound of a room using speakers playing the music and microphones picking up the results of the music played in the room with all of its additional reverberation.
Read more here: https://www.musictech.net/2018/07/essential-guide-to-reverb/