1. What does it mean?
개이득 combines the rough intensifier 개- with 이득, a benefit or gain. It celebrates coming out ahead, whether that means a useful freebie, saved effort, or a favorable result in a game.
Also written or said as gaeideuk
2. The nuance
The gain need not involve money. 개- gives it a blunt, slangy tone, so 이득이다 or 좋다 is safer in polite or professional conversation.
3. Examples
“표를 바꿨더니 더 가까운 자리라 개이득이야.”
I changed my ticket and got a closer seat. What a win.
“집 앞에 새 도서관 생긴 거 완전 개이득.”
Having a new library right by my place is such a win.
Sources
References support the meaning and usage. Example sentences are written for NoCapWiki.