Waves bounce back when they meet a surface. This phenomenon is called...

A reflection

Explanation:

Reflection – when a wave hits a surface, any part of the wave that cannot pass through the surface bounces back. This interaction with a surface is called reflection.

Another way to explain it is

Reflection occurs when waves bounce back from a surface they cannot pass through.

gas and liquid

electromagnetic shielding is the practice of reducing the electromagnetic field in a space by blocking the field with barriers made of conductive or magnetic materials. shielding is typically applied to enclosures to isolate electrical devices from their surroundings, and to cables to isolate wires from the environment through which the cable runs. electromagnetic shielding that blocks radio frequency electromagnetic radiation is also known as rf shielding.

the shielding can reduce the coupling of radio waves, electromagnetic fields and electrostatic fields. a conductive enclosure used to block electrostatic fields is also known as a faraday cage. the amount of reduction depends very much upon the material used, its thickness, the size of the shielded volume and the frequency of the fields of interest and the size, shape and orientation of apertures in a shield to an incident electromagnetic

from wikipedia