Reverberation occurs where the sound pulse bounces back and forth between two highly reflective interfaces. The equal time interval between returning reverberant signals, results in a series of equally spaced echoes distal to the deepest reflecting interface.

Example 1

This image shows a reverberation artefact seen within the liver due to sound bouncing between the transducer surface, and superficial tissue layers.

Reverberation appearances can be limited by reducing the gain settings.

Never interpret anything in the dead zone or extreme near field. 
Occurs when the ultrasound beam reflects back and forth between the structures (“reverberates”), the ultrasound transducer interprets the sound waves returning as deeper structures since it took longer for the wave to return to the transducer.
Example 2

This image shows reverberation distal to a needle during line placement.

Sound reverberates within the shaft of the needle.