Definition - What does Background Level mean?
Background level, or background radiation, is defined by the International Atomic Energy Agency as the ionizing radiation that can be found in the environment. It originates from a variety of sources, either natural or artificial, and varies in time and location. Sources include cosmic radiation, naturally occurring radioactive materials, and residue from nuclear weapons testing and nuclear accidents.
Safeopedia explains Background Level
Natural and man-made radiation come from different sources, but both affect humans in the same way. The Nuclear Regulatory Commission (NRC) regulations strictly govern the amount of radiation that can be emitted by a nuclear facility and exposure limits to workers and the general public.
Exposure to radiation from natural sources is impossible to avoid in both working and public environments. In most cases this exposure is of little or no concern, but in certain situations the introduction of health protection measures needs to be considered. In nuclear plants and laboratories with radioactive substances, protective gear is mandatory to minimize acute exposure.