A.R.M.Y is the fandom name for a popular south Korean idol group called BTS, (Bangtan Boys, Bangtan Sonyeondan or Beyond The Scene).
A.R.M.Y (아미) stands for "Adorable Representative M.C for Youth." ARMY means "military" in English. The soldiers in the military always stick together, so it means that the fans (ARMYS) will always be with the Bangtan Boys.
Kpop Newbie: I like BTS's music, but what is their fandom name?

BTS Fan: BTS's fandom name is A.R.M.Y.
by Mika Kaito December 14, 2017
1. Fans who will cut you if you say anything bad about BTS

2. People who fight for the war. Yeah, they're brave as heck.
"A.R.M.Y's are literally an Army of scary yet passionate fans"
by MayoSauce May 21, 2019
ARMY stands for adorable representative M.C of Youth.
Army is a fandom who focuses on their favs instead of focusing on other people. They know how to act mature and they love BTS with their whole heart. Army is Not just a Fandom but a family.
“Have you heard of A.R.M.Ys? I heard they are one of the biggest fandom in the world”
by arandompersonwhosaysfacts October 3, 2020
Unlike what some people think ARMY are not trouble makers nor do they cause drama or fan wars, they are simply those who supported a group of underdogs (at the time) called BTS who received a lot of hate from the kpop community because of their different approach/views and so did their fans. It stands for adorable representative MC of the youth which is eh.. Namjoon seems to like it so! They support the seven boys like no other fandom does and they conquered so so much together it's a miracle.
A.R.M.Y :
Namjoon: ARMYYYY!
Taehyung: I'm thankful for our ARMY the most, thanks to you our shoulders are held high (proud), thank you, we love you.
by Whysoprettae June 1, 2018

to be
A.R.M.Y is the eldest branch billy!!
by Fadedhonor February 24, 2018
A.R.M.Y is the fanbase name of South Korean group BTS. A.R.M.Y is an acronym for Adorable Representative M.C. for Youth. A.R.M.Y is a very loyal and passionate fandom, they are very protective of the boys due to some things that happened in the past. The fan base can be very overwhelming at first, but that is because they want to spread the boys' music and message.
Radio Host 1: omg Carl have you seen the flowers and cupcakes A.R.M.Y sent because we played Fake Love?

Radio Host 2: No, who's A.R.M.Y?

Radio Host 1: A.R.M.Y is the name of BTS' fan base, the were so happy when we played their song. They're one of the most passionate fanbases I've ever encountered.
by Esletra June 27, 2018