Killing involves the termination of life by an outside force or agent. When it is brought about by the action (or inaction) of a human being, it may be considered lawful or unlawful. It may also be considered ethical or unethical, or moral or immoral.
Killing of humans by other humans
Lawful forms of human killings may include:
- justifiable homicide, including killing in self-defense
- execution by the state
- (legally sanctioned) war
- killing sanctioned by religious authority
Unlawful human killings involving "malice aforethought" constitute murder. Unlawful human killings not involving "malice" may be termed manslaughter or homicide.
The killing of oneself is called suicide. Helping another person to commit suicide is considered unlawful in most modern societies, but not always unethical or even immoral; see the Wikipedia article on euthanasia.
The intentional killing of an unborn human fetus is called abortion. It is a very controversial subject raising many philosophical and legal issues.
Killing of non-humans
The killing of a non-human animal is almost always considered less objectionable (e.g., is more often lawful) than the killing of a human under similar circumstances. In addition, typically the "less human-like" the animal is, the more likely its killing would be lawful and not considered unethical or immoral. For example, the killing of a dog might be unlawful if it involves cruelty, while the killing of an insect or worm might be considered lawful regardless of the method used.
Killings of non-animal life are almost always lawful and considered ethically and morally neutral, except insofar as they have a negative effect on humans (e.g., damage to property, destruction of food supplies, etc.).