갑분싸 /gap-bun-ssa/
Sudden awkward silence
Short for 갑자기 분위기 싸해짐 (suddenly the atmosphere got cold). The moment when someone says something awkward and the whole vibe dies.
Examples
걔가 그 말 하고 나서 갑분싸됐어
After they said that, there was a sudden awkward silence