Toughness

Toughness is a Fallout, Fallout 2, Fallout 3, Fallout Tactics, Fallout: New Vegas, and Van Buren perk.

Fallout, Fallout 2 and Fallout Tactics
When you are tough, you take less damage. Each level of this perk adds +10% to your general damage resistance.

Fallout 3
With the Toughness perk, you gain +10% to overall Damage Resistance, up to the maximum of 85%. You will also gain a unique dialogue option when talking to Ted Strayer during the You Gotta Shoot 'Em in the Head quest.

Fallout: New Vegas
With the Toughness perk, you gain a permanent +3% to your Damage Threshold; if you take the Toughness perk a second time, this benefit increases to +6%.

Since this perk operates on a percentage, rather than a fixed value, it may be better to hold off on taking it until you acquire the NEMEAN Sub-Dermal Armor implant.

Van Buren
Even tougher than the old Toughness! No longer just bullets and punches, now you can resist fire, plasma, and grenades!

Behind the scenes
The image of this perk is a reference to Superman.