D3X is was used as a shorthand term for an "Diablo 3 expansion."

Though no The term was created prior to the release any such product officially existsexisting. At the time, Blizzard has had frequently commented on their plans for at least two [[expansion]] packs for Diablo III, and since the Diablo II expansion, [[Lord of Destruction]], was widely-known as D2X, this acronym for the Diablo III expansion seems inevitable.  The expansion pack eventually became [[Reaper of Souls]].