An ARG stands for:
Alternate
Reality
Game
It isn't really bad, it's most of the time something made to scare people, sometimes they include riddles people need to solve.
The ARG's already probably got finished, and the winners are me, Woofla (One of Retro's boyfriends) and Tasque_Manager (A character from Deltarune chapter 2), we get to know who the alts are under one condition: We must never tell anyone.