1. What does it mean?
갬성 is a deliberately altered spelling of 감성. In captions and conversation it often points to a pleasing or distinctive atmosphere: nostalgic photographs, cozy interiors, music, or a carefully styled scene.
Also written or said as 갬성적, gaemseong
2. The nuance
It can be sincere, teasing, or ironic about an overly curated aesthetic. Unlike a formal discussion of 감성, the altered spelling foregrounds an informal internet voice.
3. Examples
“흔들린 필름 사진도 나름 갬성이 있네.”
Even this blurry film photo has a vibe of its own.
“비 오는 날 이 노래를 들으니까 갬성이 달라.”
Listening to this song on a rainy day gives it a different mood.
Sources
Sinjoeo Korean Slang Dictionary
References support the meaning and usage. Example sentences are written for NoCapWiki.