1. What does it mean?
댓삭 shortens 댓글 삭제. It describes the removal of a reply or comment, rather than the entire original post.
Also written or said as 댓글 삭제, daetsak
2. The nuance
The action may correct an error, protect privacy, or follow moderation. 댓삭튀 is a more judgmental form implying someone deleted a comment to dodge a response; that motive is not inherent in 댓삭.
3. Examples
“다른 글에 달 댓글을 잘못 써서 댓삭했어.”
I posted a comment meant for another thread, so I deleted it.
“오타 수정이 안 돼서 댓삭 후 다시 남겼어.”
I couldn't edit the typo, so I deleted the comment and posted it again.
Sources
Sinjoeo Korean Slang Dictionary
References support the meaning and usage. Example sentences are written for NoCapWiki.