Snap (Earth-1600)

The Decimation was a massive genocide of half of all life within the universe planned and executed by Thanos who successfully gained all the Infinity Stones and activated them in the Infinity Gauntlet.

Trivia

 * The term "decimation" is formally used to define "the killing of one in every ten of a group of people as a punishment for the whole group." This, therefore, makes the term a formally incorrect description for an event in which 50% of life was killed.
 * The term is likely similar to the Decimation storyline, where Scarlet Witch used her powers to de-power a massive majority of mutants.