The slang term 남사친 (namsachin) refers to a male friend who is strictly platonic—not a boyfriend.
It’s a combination of:
남 (nam) → Short for 남자 (namja), meaning “man”
사 (sa) → Short for 사람 (saram), meaning “person”
친 (chin) → Short for 친구 (chingu), meaning “friend”
So, 남사친 literally translates to “male-person-friend”, distinguishing a male friend from a 남친 (namchin), which means “boyfriend”.
Note the different writing!
남사.. vs. 남자.. 남사친 = platonic male friend, 남자친구 = boyfriend
Example Sentences:
그는 내 남사친일 뿐이야. He’s just my male friend.
남사친이랑 영화 보러 갔어. I went to watch a movie with my male friend.
남사친하고 여행 가는 건 어때? How about going on a trip with your male friend?
The female version of this word is 여사친.