Reverb is short for the word reverberation. It's a method of adding "life" to an otherwise lifeless recording.
You hear reverb mostly on voices. Recording studios add it when the original voice recording was made devoid of any room interactions.
To explain reverb in another way, it's created when a sound or signal is reflected off the room or objects in the room, built-up, and then decayed as the sound is absorbed by the surfaces of objects in the space.
A long and complicated way of saying it's the difference between walking into an acoustically dead or alive room. The differences being how sound is reflected or absorbed.
When I walk into a new room I am always listening for how that room interacts with my voice: alive or dead. Perfect rooms don't suck away sound nor do they overly reflect it.
Reverb is that essential element in any listening environment.
The element that brings acoustic life or death.
