What does "background radiation" refer to?

Background radiation refers to the natural radiation present in the environment that we are continuously exposed to, regardless of specific human-made sources of radiation. This type of radiation comes from various natural sources, including cosmic rays from outer space, terrestrial radiation from radioactive materials in the earth, and even radon gas that can accumulate in buildings.

The reason this option is the correct answer is that it encompasses all the holistic sources of radiation that exist in our daily environment, including cosmic and terrestrial origins, which contribute to the baseline levels of radiation we experience. Understanding background radiation is crucial for radiation safety practices, as it establishes a baseline against which other radiation exposure can be measured.