Multiple echoes or reflections; in ultrasonography, an artifactual image caused by delay of an echo which has been reflected back and forward again before returning to the transducer. Reverberation is the persistence of sound in a particular space after the original sound is produced. A reverberation, or reverb, is created when a sound is produced in an enclosed space causing a large number of echoes to build up and then slowly decay as the sound is absorbed by the walls and air. This is most noticeable when the sound source stops but the reflections continue, decreasing in amplitude, until they can no longer be heard. The length of this sound decay, or reverberation time, receives special consideration in the architectural design of large chambers, which need to have specific reverberation times to achieve optimum performance for their intended activity. in comparison to a distinct echo that is 50 to 100 ms after the initial sound, reverberation is many thousands of echoes that arrive in very quick succession (.01 – 1 ms between echoes). As time passes, the volume of the many echoes is reduced until the echoes cannot be heard at all. An OSH glossary used in safety and health at work which is, adopted by ILO {102}. The term definition has been obtained from the secondary source