What is reflection of sound (echo) ?

Reflection of sound:
When Sound is incident on the surface of the medium it bounces back into first medium .This phenomenon is called echo or reflection of sound.
The sensation of sound persists in our brain for about 0.1s.To hear clear echo,the time interval between our sound and the reflected sound must be at least 0.1 s.If we consider speed of sound 340ms at the normal temperature in air ,we will hear echo after 0.1 s. Echoes may be heard more than once due successive or multiple reflection.