Killing Curse

Avada Kedavra is the incantation for the Killing Curse, one of the Unforgivable Curses. When spoken, the caster's wand shoots out a jet or green light, which, when it comes in contact with the target, results in the target's instant and painless death. Voldemort is known to have used the Killing Curse frequently. There is no known counter-curse for the spell; the only known defences against it are dodging the spell, hiding behind a physical barrier (which is destroyed upon impact), creating Horcruxes, and the voluntary self-sacrifice of a relative, which causes ancient magic to protect the intended victim from the curse.

Only one person is known to have survived the curse: the young Harry Potter was saved when his mother, Lily Potter, decided to block the curse herself instead of having her son killed; when the curse used on Harry rebounded, Voldemort's body was destroyed, but, owing to his many Horcruxes, his spirit was unable to leave the physical world, and was later placed in a new body identical to his old one.

Etymology
Avada Kedavra may ultimately come from the ancient Aramaic language, unlike Rowling's other spells, which derive from Latin. Avada Kedavra may come from the conjurer's word "abracadabra" (from Aramaic avra kedavra "I create as I speak"). Rowling may have taken her spell from a form such as avara kedavra or "I destroy as I speak", which differs from the "I create" form in just one letter.

People killed with Avada Kedavra

 * James Potter
 * Lily Potter
 * Amelia Bones
 * Frank Bryce
 * Cedric Diggory
 * Albus Dumbledore
 * Voldemorts Grandparents
 * Tom Riddle Senior.
 * A spider