Voldemort is a taboo in the wizarding world—a taboo whose very name cannot be spoken aloud, which alone speaks volumes of his terrifying reputation.
However, he has been gone for more than a dozen years. Therefore, although his name remains a taboo for the vast majority of people—as if uttering it would bring immediate misfortune—many have actually slowly forgotten him.
Of course, there are those who have not forgotten him yet still do not take him seriously, though those are ultimately rare exceptions. That said, those exceptions happen to be a tiny bit numerous at Hogwarts.
Chapter 302