A recently released Marvel Cinematic Universe young adult novel titled Marvel's Avengers: Infinity War: The Cosmic Quest Vol. 2: Aftermath gives an in-universe name to Thanos' Avengers: Infinity War "snap", according to ScreenRant.
The novel reportedly refers to "the snap," in which Thanos snapped his fingers using the Infinity Gauntlet to wipe out half the life in the universe, as "the Decimation."
If that name sounds familiar, in comic book lore, "Decimation" is the name given to Scarlet Witch's "no more mutants" spell from House of M, which reverted many mutants into homo sapiens.
The name "Decimation" for the "snap" remains unconfirmed as MCU nomenclature - but with the destructive nature of the comic book story of the same name, it's entirely possible that the terminology could make its way into official big screen MCU use.
The still untitled Avengers 4 is due out in theaters May 3, 2019.