Apo! Bangpo!

This word was created by Jeon Jungkook, the youngest member(maknae) of BTS (a boyband from South Korea). The word "Apo! Bangpo!" translates to the short form in Korean for "ARMY forever, Bangtan forever".

(PS: ARMY is BTS's fandom name, and Bangtan sonyeondan is what BTS stands for).

For instance;

ARMY uses "Apo! Bangpo!" among themselves and to towards BTS to show affection. BTS too uses this to express their love towards fans.