Rapid Healing is one of Fallout GURPS advantages. See: Fallout GURPS.
This advantage is only available if your basic HT is 10 or above. You recover rapidly from all kinds of wounds. Whenever you roll to recover lost HT, or when you roll to see if you can get over a crippling injury, add 5 to your effective HT. This ability does not help you get over stunning or similar incapacities.”— Steve Jackson Games GURPS sources
With the abandonment of GURPS, Rapid Healing was recycled, image reused for healing rate.