1. A structure of dense material; such as, concrete or lead, around a nuclear reactor to protect against radiation.
2. a mass of absorbing material; for example, concrete or lead, placed around a reactor or radioactive material to reduce the radiation to a level safe for humans.

A housing, usually aluminum or copper, placed around a circuit to prevent interaction with other circuits by providing a low resistance and a reflecting path to ground or high-frequency radiation.

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.

1. A shield that prevents electrostatic coupling between circuits, but allows electromagnetic coupling.
2. A metallic enclosure or screen placed around an apparatus so it will not be affected by external electric fields.
3. A grounded metal screen, sheet, or enclosure placed around an apparatus or between two appliances to prevent electric fields from acting through the shield.

It can prevent interaction between the electric fields of adjacent parts on a chassis.

The layer of ozone which hangs in the atmosphere from 20 to 40 miles above the surface of the earth and protects the earth from excessive ultraviolet radiation.

Some experts claim that the manufacture of various chemicals; such as, chlorofluorocarbons used as propellants in aerosol sprays, and the effects of high-flying jet aircraft are destroying this protective layer and allowing excessive amounts of ultraviolet radiation to penetrate the earth's atmosphere; therefore, subjecting humans to increased dangers of skin cancer and other health problems.