문경지교가 · 문경지교를
a friendship so deep you'd die for each other
Example
두 장군은 문경지교를 맺은 사이로 유명합니다.
The two generals are famous for a friendship they'd die for.
Word parts
문 cut+경 neck+지 of+교 friendship
Literally 'a neck-cutting friendship': friends willing to lose their heads for each other.