echo:
If the reflected sound is heated separately from an original sound, then the reflected sound is called an echo of the original sound.
reverberation:
It is often noted that when a loud sound is produced near the walls of a big hall, it returns after being reflected very quickly (time interval is less than 1/10 s) when the effect of the original sound still persists. On account of successive reflections from the walls, a continuous rolling of sound goes on for some time. This persistence of sound due to multiple reflections from the walls is called reverberation.