1. What does it mean?
Combining 갓, from the English word “god,” with the Sino-Korean 생 (生, “life”), 갓생 describes a diligent, well-organized life. People also use it for an especially productive day or for keeping a modest self-improvement routine.
2. The nuance
It is often encouraging or knowingly exaggerated. Calling a day 갓생 does not require a spectacular achievement; the standard depends on the speaker and the context.
3. Examples
“오늘 일찍 일어나서 운동까지 했어. 나 좀 갓생 사는 듯?”
I got up early and even worked out. I'm having a pretty productive day, aren't I?
“이번 주는 제때 자는 것부터 갓생 시작해 볼래.”
This week, I'll start building better habits by going to bed on time.
Sources
National Institute of Korean Language
References support the meaning and usage. Example sentences are written for NoCapWiki.