Toughness (GURPS) is one of Fallout GURPS advantages. See: Fallout GURPS.
Your skin and flesh are tougher than the average human's. Your body itself has a Damage Resistance (DR) score. This DR is treated just like the DR from armor: you subtract it from the damage done by any blow before you multiply the damage done by a cutting or impaling weapon.”— Steve Jackson Games GURPS sources
With the abandonment of GURPS, Toughness (GURPS) was recycled into the Toughness perk.