I am really really really really not sure of this, I saw it around the net.
So, A.R.M.Y means
Adorable representive M.C for youth.
idk .... weird right. That's why I am not sure of it.
So another meaning is that we are strong, like military army. We will always be bulletproof.
I am waiting for the members to confirm this or even if Bighit confirms it.
Further information about the fandom name will be updated later ^^