Reverberation is the persistence of sound in an enclosed or partially enclosed space after the source of sound has stopped; by extension, in some contexts, the sound that so persists.
Reverberation consists of sounds that have been reflected many times and come at the listener from many directions. Rooms with excess reverberation may be called boomy or lively (such as churches and gymnasiums), while rooms with little reverberation – like recording studios – are "dead."
Reverberation time is an acoustical measure of how quickly sound diminishes in a particular space; tailing off of a sound in an enclosure because of multiple reflections from the boundaries.
Artificial reverberation is reverberation generated by electrical or acoustical means to simulate that of concert halls, etc., added to a signal to make it sound more lifelike.
A reverberation room is a room so designed that the reverberant sound field closely approximates a diffuse sound field, both in the steady state when the sound source is on, and during the decay after the source of sound has stopped.