A metal screen or enclosure placed around circuits to reduce the effects of both electric and magnetic fields.

Electromagnetic fields are caused by motors, generators, relays, or devices whose operation dempends on alternating fields.

Shielding is achieved by a reflection or absorption of fields while reflection occurs at the surface, and it is not usually affected by shield thickness.

Absorption, however, occurs within the shield and it is highly dependent on the thickness of the shield.