The difference between manslaughter and murder, of any degree, is the issue of premeditation. The intent to kill determines whether it is appropriate to class a homicide as murder, according to The Economist, with manslaughter being reserved for unintentional, or even accidental, killing.
Murder is a moral and legal concept that covers the unwarranted taking of human life under circumstances other than self-defense and with the intent to kill. Typically, first-degree murder entails serious premeditation, while second-degree murder can be incidental to other actions such as a fistfight.
Manslaughter is a lower grade of homicide that usually omits considerations of intent. In manslaughter cases, the accused's actions led to death, and the events were preventable and under the control of the accused, but the accused lacked the specific intent to kill and was not reckless to the degree implied by second-degree murder charges, notes The Economist.
An example of first-degree murder is that of an assassin lying in wait with clear intent to kill, while a second-degree murder could take the form of a drunk and angry assailant hitting the victim with a chair. In the second case, the assailant may not have intended to kill but intentionally inflicted injuries that could lead to death. An example of manslaughter is that of a doctor who is grossly negligent but lacks the intent to do harm.