What does radon exposure mean?

Radon. Radon is a gas that can be emitted from soil e.g. Under houses and can accumulate. The radon gas is toxic. Radon exposure means that someone or something has been subjected to radon gas.
Radiation. One form of radiation emission from radium is via radon gas. While few ever get exposure, many home sites are built on areas where radon gas can be detected such as in the basements. This exposure can lead to the appearance of malignancies. Many homes have been tested for such emission. Kits are available for such testing.