When the vibe/mood/aura of a room/place seems uneasy and out of the ordinary, the air is heavy and something feels wrong. It commonly foreshadows that something terrible is about to happen.
The term was heavily popularized in 2017 when the game DDLC (Doki Doki Literature Club) was released, and one of the characters (Yuri) uses it.
Once a month a man will ejaculate all over himself as his genitils excrete all of last month’s semen. After he has cum all over himself he will start to produce new semen for the month.