Radiation. A measure of the activity of atomic molecules in something. And bad for you. Collecting rads is a bad habit, and will kill you, very quickly.
Radiation is gained by
- Swimming in irradiated water (Stupid)
- Standing in irradiated Zones (Stupid)
- Eating irradiated food (Stupid)
- Drinking from toilets (so amazingly fucking stupid that we shouldn't even have to tell you)