Euthanasia
Euthanasia is when a person's life is purposely ended because of disease or pain, which has made them suffer. This is different from assisted suicide, where a person helps someone kill themselves. It is also different to murder, where the reason is not suffering, but to kill for the killer's own ends. Euthanasia can be voluntary, where the person who dies asks for help in ending their life. Where the person is unable to make their decision known, it is usually called non-voluntary euthanasia.  Where someone is killed against their will, it is usually called murder.