Manslaughter is the unlawful killing or homicide of a human being without the premeditation or malice (malice aforethought) required for the criminal offense of murder. Many states have two types of manslaughter: (1) voluntary manslaughter—the defendant intended to kill the victim, but did so in self-defense, or in the heat of passion and without premeditation, or the defendant was insane and did not understand that the killing was wrong; and (2) involuntary manslaughter—the defendant negligently or recklessly caused the death of another person—such as when a person is intoxicated while operating a motor vehicle and causes an accident that results in the death of another person.

Some states do not have separate criminal offenses for voluntary and involuntary manslaughter—these states may have the offense of manslaughter and identify certain aggravating factors that may enhance the penalties upon a conviction for manslaughter. Manslaughter is a felony offense and may be punished by a lengthy prison term. Manslaughter laws are generally located in a state's statutes—often in the penal or criminal code.

In Oregon, manslaughter is categorized into degrees and is defined under Oregon Revised Statutes (ORS) 163.118 and 163.125. Voluntary manslaughter is not specifically termed as such in Oregon law, but the concept is similar to what Oregon defines as 'Manslaughter in the First Degree' (ORS 163.118). This occurs when a person intentionally causes the death of another under circumstances that do not constitute murder because they acted under the influence of an extreme emotional disturbance. Involuntary manslaughter aligns with 'Manslaughter in the Second Degree' (ORS 163.125), which occurs when a person causes the death of another person recklessly, with an awareness of and conscious disregard for a substantial and unjustifiable risk, or by causing the death of a dependent person through neglect or maltreatment. Both degrees of manslaughter are considered felonies in Oregon, with Manslaughter in the First Degree being a more serious offense and carrying a longer potential prison sentence than Manslaughter in the Second Degree. Aggravating factors, such as the victim being a child or a vulnerable person, can increase the severity of the charges and penalties.