Homicide is defined by Merriam-Webster's 11th Collegiate Dictionary as "a killing of one human being by another".

There are at least four kinds of homicide: murder, manslaughter, non-criminal homicide, and homicide committed by victim or victims (suicide).

Murder is the unlawful killing of another human being with intent.

Manslaughter is a legal term for the killing of a human being, in a manner considered by laws as less culpable than murder. It has two distinct categories: voluntary manslaughter and involuntary manslaughter. Voluntary manslaughter occurs when the defendant kills with malice aforethought (intention to kill or cause serious harm). Involuntary manslaughter is the unlawful killing of a human being without malice aforethought.

Non-criminal homicide
Homicides do not always involve a crime. Sometimes the law allows homicide by allowing certain defenses to criminal charges. One of the most recognized is self-defense, which provides that a person is entitled to commit homicide to protect his or her own life from a deadly attack.