An extinction event refers to a catastrophic event that leads to the extinction of a large number of species. Some synonyms for the term include mass extinction, biological crisis, ecocide, and die-off. A mass extinction refers to a situation where a significant proportion of species on earth go extinct in a short period. Ecocide refers to the deliberate or accidental destruction of the environment, leading to the extinction of plant and animal species. A biological crisis refers to the collapse of ecosystems, leading to a decline in species populations, while a die-off refers to a sudden extinction of an entire population of a species.