The slang term 여친 (yeochin) is a shortened form of 여자친구 (yeojachingu), which means “girlfriend.” It is commonly used in casual conversations and text messages.
Note the different writing!
여사.. vs. 여자.. 여사친 = platonic female friend, 여자친구 = girlfriend
Example Sentences:
여친친이랑 데이트했어. I went on a date with my girlfriend.
내 여친은 정말 다정해. My girlfriend is really sweet.
여친이 생겼어! I got a girlfriend!
여친이랑 여행 가고 싶어. I want to go on a trip with my girlfriend.
The male equivalent is 남친 (namchin) boyfriend.