Reverb is a very tight echo type sound that is the persistence of audio after it is produced.
Listen carefully to a lot of radio sweepers and you’ll hear they are laden with reverb to give a good sound. Reverb can add a polish to your production but in addition to just adding a nice warm trailing reverb sound to your audio reverb can also be used to bring in your audio as well making a more dramatic sweeper.
Reverb can also be used to bring in music and to provide a “false” ending to music as well.
Reverb can also occur in audio when we don’t want it to and that’s when recording in an untreated or poorly treated room. This is unwanted and very hard to remove!