The radioactive particles that settle to the ground after a nuclear explosion; SYN. radioactive dust.
Harmful radioactive material released into the atmosphere in the debris of a nuclear explosion (see nuclear warfare) and descending to the surface of the Earth. Such material can enter the food chain, cause radiation sickness, and last for hundreds of thousands of years (see half-life).

Any failure of components that occurs while equipment is being burned in, especially when the test is done at the factory. See also burn in (definition 1).