Avada Kedavra comes from the Harry Potter series, where it is the Killing Curse, one of the three Unforgivable Curses, and is most famously associated with Lord Voldemort. In the stories it causes instant death without leaving a mark, which made it the darkest spell in that world and a shorthand for absolute finality. As the films and books spread worldwide, fans began lifting the incantation for short edits, reaction videos, and gaming clips, where its two words alone signal that something is finished. That instant recognition keeps it in regular use years later.