"Best Friend" is "절친"(chŏl-chin) in Korean.
The Jeolchin (절친), I say a "friend of the close relationship to more than best friends." 절친한 stands for (Jeolchinhan, very close) + 친구 (Chingu, friend). In terms of English, become Best Friend (best friend, 베스트 프랜드, 베프).

The Jeolchin (절친), I say a "friend of the close relationship to more than best friends." 절친한 stands for (Jeolchinhan, very close) + 친구 (Chingu, friend). In terms of English, become Best Friend (best friend, 베스트 프랜드, 베프).