1. What does it mean?
트친 shortens 트위터 친구. It refers to someone you know through exchanges on Twitter, now also called X, rather than necessarily a friend you have met offline.
Also written or said as teuchin
2. The nuance
The word retains the older platform name. A 트친 relationship may be close or loose; it does not by itself imply private contact or permission to share someone else's posts.
3. Examples
“트친이 추천한 책을 읽고 감상을 주고받았어.”
I read a book a Twitter friend recommended, and we exchanged thoughts.
“오래 얘기하던 트친을 전시회에서 처음 만났어.”
I met a longtime Twitter friend in person for the first time at an exhibition.
Sources
References support the meaning and usage. Example sentences are written for NoCapWiki.