The term terror radius is most closely associated with Dead by Daylight, where it signals that the killer is nearby and pressure is building. That gameplay cue became popular outside the game in memes, streams and short edits because viewers instantly read it as a warning that something bad is coming. It still gets reused in horror content, stealth jokes and reaction clips for the same reason sounds like a danger alarm sound effect meme keep working: they create suspense before the reveal.