Invulnerability is the power to be immune to conventional harm. Characters with such powers may simply be unaffected by normal attacks, necessitating the use of things like Durability Negation to get through. Others have more conditional invulnerability, such as one that just prevents harm from conventional weaponry, but can be easily circumvented by supernatural abilities. It can be considered the defensive equivalent of Durability Negation, negating simple Attack Potency, though one should be careful not to apply No Limits Fallacy.
This is distinct from simply particularly high durability, which may make a character seem invulnerable to weaker opponents. Only characters whose invulnerability is clearly more than simply being exceptionally durable for the verse's setting qualify.