1. What does it mean?
Literally 'fishing,' 낚시 can describe online bait: a misleading title, claim, or setup that draws a person in. 낚였다 means the speaker fell for it.
Also written or said as 낚시글, 낚였다, clickbait
2. The nuance
It may refer to a harmless joke, an exaggerated headline, or more serious deception; the word alone does not distinguish them. A 낚시 제목 is a baiting title, while a literal fishing trip also uses 낚시. Look at what the person was drawn into.
3. Examples
“제목만 보고 눌렀는데 내용이 달라서 낚였어.”
I clicked because of the headline, but the content was different. I fell for the bait.
“진짜 공지인 줄 알았는데 친구가 만든 낚시 글이었어.”
I thought it was a real notice, but it was a prank post my friend made.
Sources
KoreanClass101: Korean language lessons
References support the meaning and usage. Example sentences are written for NoCapWiki.