Homicide is the formal term for one person killing another person, whether the act was criminal or not. There are four legal categories of homicide, which vary in their definitions and associated punishments from country to country.

The main categories of homicide are murder, which denotes a crime committed with malicious or clear intent; manslaughter, which includes acts committed in a moment of passion or recklessness without malice aforethought; noncriminal homicide; and excusable, negligent, or accidental homicide, such as when someone dies during surgery due to unforeseen complications.

In the United States, the categories of murder and manslaughter are subdivided into levels of seriousness, or "degrees."

Homicides generally not regarded as criminal are those committed in self-defense, to aid a police officer or other representative of the law (for instance, during a sanctioned execution), or to stop someone from committing a serious crime. In addition, the legal systems...