Known as 'Reverb.' this is the persistence of a sound beyond the initial sound that was produced and is characteristic of spaces and surfaces. Natural Reverb. is really very a series of fast echoes therfore hard surfaces and not-too-large a venue produces the best reverb. Soft furnishings tend to absorb sound rather than reflect and large venues echo due to the longer delay.
In recording studios there is often a conflict between sound dampening to avoid extraneous sounds and achieve a pure recording of a voice or instrument and the warmth that reverberation gives with the impression of spatial ambience. Thus reverb. is available as an electronic effect which can be applied at the Mixing Desk. It is also available and widely used as an effects pedal.
Early artificial reverberation used real spaces as 'echo chambers' with a loudspeaker and a microphone. Later ones used physical material such as plates or springs to provide a delay to the signal or sound. Modern reverb. is a digital electronic effect even down to the synthesis of plate and spring-line units or the effect of a certain type of venue such as hall, auditorium or even tiled bathroom.