Fighting (also written as hwaiting sometimes, due to the lack of the [1] sound in Korean) is word used to support someone. The definition of this term is further expanded on the Korean Language Blog:

“Far from a battle cry, 화이팅 hwaiting is a commonly used word of encouragement, as well as a cheer. I’m told it made its way into Korean from its obvious English origin via the Japanese—and hence the unusual pronunciation. Language purists insist that it should be spelled 파이팅 paiting to reflect a closer approximation to the English word fighting. (As I typed 화이팅 above, and again here, the spell check tried to change it to 파이팅!) However, it’s universally pronounced hwaiting and so you will encounter both spellings. Although in use for decades, it’s inclusion into dictionaries has been met with some reluctance, still considered merely slang.

You’ll often hear Koreans try to translate 화이팅 as fighting, understandably, but we can actually translate it a couple of ways, depending on the situation…

At sporting events, the crowd will cheer on their team with 화이팅, sometimes preceded by 아자, 아자! aja aja! just to get pumped up, and in international matches: 대한민국, 회이팅!! daehanmin-guk, hwaiting!! or even 코리아 화이팅!!koria hwaiting!! Go, Korea!!”