- A region of charged particles that surround a celestial body possessing magnetic fields.
- Each of the two regions of ionizing radiation which surround the planet earth, and which interact with its magnetic field. These belts are composed mostly of protons and electrons which originate from the solar wind which become trapped by the earth's magnetic field. These two belts extend from about 700 kilometers to beyond 50,000 kilometers, and their contained particles travel along the planet's lines of force. Also called Van Allen radiation belt.