BTS stands for Bangtan Sonyeondan for Korean ARMYs, Beyond The Scenes for US ARMYs (for most at least), or Bangtan Boys Bulletproof Boyscouts/ Bodan Shonendan for International fans. You might be wondering why it stands for more than one thing. 

http://bts.ibighit.com/

BTS

-27%
-18%
-26%
-33%
-25%
-60%
-24%