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 New Hampshire, manslaughter is categorized under RSA 630:2 as either 'Manslaughter' or 'Negligent Homicide.' Manslaughter in New Hampshire is defined as causing the death of another under circumstances that do not constitute murder, often involving a level of recklessness or negligence but lacking the premeditation or malice aforethought required for a murder charge. Voluntary manslaughter typically involves a killing in the heat of passion or as a result of provocation, whereas involuntary manslaughter usually involves unintentional killing resulting from reckless or negligent actions, such as a fatal car accident caused by a drunk driver. New Hampshire law does not explicitly divide manslaughter into voluntary and involuntary categories but does distinguish between different levels of culpability and circumstances surrounding the unlawful killing. Manslaughter is considered a felony in New Hampshire and can result in a significant prison sentence, with the exact penalties varying based on the specifics of the offense and any aggravating factors present.