The "Killing Curse," known as Avada Kedavra, is one of the three Unforgivable Curses in the Harry Potter series created by J.K. Rowling. When cast, it causes instant death to the victim without any physical harm or injury. The curse is characterized by a flash of green light and is considered one of the darkest forms of magic. Using the Killing Curse is illegal and morally reprehensible in the wizarding world. It requires a strong intent to kill, making it a reflection of the caster's will. Those who use it can face severe consequences, including a life sentence in Azkaban, the wizarding prison.