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.
“Stagnating air is common foreshadowing that something terrible is about to happen” -Yuri 2017
by TheFrenchDuck June 1, 2021
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is common foreshadowing that something terrible is about to happen
-Yuri from Doki Doki Literature Club
stagnating air
by f1n3 is not a n00b February 27, 2021
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