In general, vehicular homicide is the unlawful killing of another human being with a motor vehicle. It's not considered murder unless there was provable intent to kill. However, "vehicular homicide" can refer to murder, manslaughter, or negligent homicide -- the only difference here is that a vehicle is the weapon used to kill another person, whether intentionally or unintentionally. However, some degree of negligence, reckless behavior, or intent to harm while driving is what brings on a charge of vehicular homicide.
The precise definitions and punishments for vehicular homicide vary by state/nation and the circumstances of the killing. Some states also consider a homicide caused by a person piloting an airplane or watercraft to be vehicular homicide.
For instance, Georgia classifies vehicular homicide as being first degree or second degree depending on the driver's role in causing the death.
First degree vehicular homicide in that state involves the perpetrator fleeing the scene, being under the influence of drugs or alcohol, or driving recklessly to cause the accident. For instance, a death caused by someone illegally drag racing or playing chicken would result in a first-degree charge. A first-degree offense in that state is a felony that can result in up to 15 years in prison.
Second degree vehicular homicide in Georgia is a misdemeanor. A person may be charged with it if they kill someone due to momentary inattention or a simple traffic infraction such as speeding or running a stop sign -- the line between a simple traffic infraction and reckless driving might be in the eye of the beholding judge, but the consequences are important. A person who has a history of traffic accidents or DUIs will often get the more serious charge automatically, regardless of the specifics of the accident at hand. A person convicted of the misdemeanor version may face a jail term of up to 1 year or a fine of up to $1,000.
Thus, in magicmanzach's situation, his fleeing the scene raised his potential criminal charges from a misdemeanor to a felony, if the accident had happened in Georgia or a state with similar laws.
In some states such as Indiana, pedestrians always have the right of way. Thus, if you hit a pedestrian in such a locality, you will almost certainly be charged with vehicular homicide if they die, even if the pedestrian did something reckless like dart out into traffic. When faced with such a charge, you will have to prove beyond a doubt that you were paying full attention and had no way to avoid hitting the person.
As with other forms of homicide, there is no statute of limitations on someone receiving criminal charges due to a vehicular homicide in the U.S. If someone flees the scene of a deadly collision, they may be charged later, even many years later, if sufficient evidence of the crime comes to the attention of the police.