Damage is frequently done to characters that should hurt or incapacitate them, but is easily shaken off. Nobody ever breaks a rib or other bones unless that specific broken bone becomes important later on.
This isn't Super Toughness or Nigh-Invulnerability, where the character is supernaturally protected from harm. This is the ability to shrug off blows that would disintegrate a human body when you technically shouldn't be able to do so. Robots, Mutants, Mages, Ki using Martial Artists, etc. do not count. Having a story-enabled reason for not being a bloody smear immediately takes one out of the running for this trope.
Certain Required Secondary Powers may also induce this and it is particularly true for Super Hero characters to have "increased strength and endurance" in their portfolio, even if never outright explained or stated. How else can someone whose sole power is throwing flame take being thrown off a multi-story building as no big deal? The line gets fuzzy between Badass Normal and Charles Atlas Superpower where somehow a "normal" person has become invulnerable to the effects of injury by willing themselves uninjured. Modern special effects are somewhat to blame for this, as they frequently up the forces involved to look more dramatic. This sometimes approaches cartoon-esque extremes, such as a person getting smashed through concrete or brick walls and being able to get right back up again with only negligible injury.
By extension, blunt damage, concussions, and other side effects of "non-lethal" fights or a Tap on the Head never have unintended fatal consequences — death can only happen with intentionally-lethal weapons, like swords or guns. Even with normally-lethal weapons, the hero may intentionally inflict flesh wounds instead of shooting to kill.
This trope also enables our hero to take a bullet in some critical area (chest, shoulder, etc) and continue to fight as though nothing had happened, even if they should be Overdrawn at the Blood Bank.
It makes you wonder why, for all the supposed beatings they have received themselves over the course of a show, the hero/heroine never suffers any long-term scarring or lasting physical injury. One especially tenacious example is the lack of punch drunkenness. Indeed, unrealistic lack of damage from head injuries leads to the widely prevalent Sub-Trope: Hard Head.
Punch-drunk boxers are the classic Real Life example of what happens to someone who takes repeated pummeling damage in many fights year after year. However, the American National Football League presents a better sampling. To survive more than a couple of seasons in the league is a guarantee of a lifetime of painful, lingering damage to battered joints, bones, and connective tissues. That life is also going to be about ten years shorter than that of the average adult American. The heart and body organs build up scar tissue likely to fail when the athlete is in his fifties and sixties. This condition is known as Dented Iron.
Between them, Made of Iron and Hollywood Healing cover the two main varieties of action hero — the Terminator-type that can walk unscathed through a bomb-blast, and the hero who does get hurt badly but somehow always comes back to triumph in the end.
The polar opposite of this is Made of Plasticine. A character who doesn't just shrug off extreme damage, but doesn't sustain any damage at all, is Nigh-Invulnerability. Characters who are Made of Iron, if they die at all, often die Rasputinian Deaths. If two Made of Iron characters go up against each other, it often leads to How Much More Can He Take? fights.
A character who is Made of Iron isn't necessarily literally made of iron. If he happens to sink in water and die as if he were, that's Super Drowning Skills.
If a person has this kind of durability as a superpower, it's Super Toughness. When the character does sustain grisly, incapacitating injuries but keeps going anyway, it's Normally, I Would Be Dead Now. If the character's durability is justification for putting them through a lot of physical stress for the audience's amusement, you probably have an Iron Butt-Monkey.
See also Charles Atlas Superpower, as being Made of Iron is one of its more common effects.
Not to Be Confused with Maid of Iron in any variation.
