Radiated

Your character is suffering from a significant amount of Radiation poisoning. The more radiation, the deadlier the effect.

More information

You could get radiated not only by being in the wrong place but also for being bitten by some creature in the wasteland (like Centaur). The more radiation your character receives the lower it's SPECIAL becomes. After receiving a large amount of radiation your character dies.

Radiation resistance reduces the amount of radiation your character is being exposed to. Rad-X can improve radiation resistance.
Radiation poisoning can be cured with RadAway or intervention of a doctor in one of the cities.