An existential catastrophe is an event that destroys humanity's long-term potential.
The concept of an existential catastrophe may be distinguished from two other concepts with which it is sometimes conflated. First, existential catastrophes differ from human extinction. An existential catastrophe need not involve the extinction of all humans, since humanity's potential can fail to be fully realized even if our species survives indefinitely (see the typology in the section below for examples).
Second, existential catastrophes differ from catastrophes involving what is loosely referred to as "the end of the world". By this expression it is generally meant some form of civilizational collapse. To amount to proper existential catastrophes, however, such catastrophes need to meet two additional conditions: first, the collapse must be global, and secondly, it must be irreversible. (If the first, but not the second, condition is satisfied, the scenario falls under the category of a global catastrophe.)