What is it called when a seismic wave bounces backward when it reaches a boundary?

When a seismic wave 'bounces backward' and reaches a boundary, it is called Reflection.

Explanation:

The seismic waves are the result of the landslides, earthquakes, volcanic eruptions, explosions by humans. They are the energy waves which travel through the earth's layers. To study the interior of the Earth, reflection of seismic waves is studied. When a wave reaches a 'boundary', there can be infinite paths it can take while bouncing back. This process is called reflection. Each path is noted with a 'set of letters' describing the phase and the trajectory. The 'upper case' represents the transmitted waves and the 'lower case' represents the reflected wave.