In: Biology
Voluntary simply means which is done deliberately while involuntary is against your own will.
While both are called manslaughter, they are extremely different. Voluntary manslaughter usually involves a killing in the heat of the moment. For instance, if Adam impulsively grabs a fire iron and fatally clobbers Bill during a sudden quarrel, the offense would likely be voluntary manslaughter. The idea is that if Adam is driven by the "heat of passion," it lessens the moral blame, so he shouldn't be charged with murder, even in the second degree.
In contrast, involuntary manslaughter concerns accidental deaths, such as traffic fatalities caused by impaired drivers. Also, it's generally considered murder, not manslaughter, to kill someone unintentionally while committing a robbery, kidnapping, or other "inherently dangerous" felony.
An example would be robbers attempting to flee from the scene of a crime who run over a pedestrian while being pursued by police officers in a high-speed chase. Even though the pedestrian's death was accidental, it would likely be charged as murder because it occurred in connection with a robbery. However, most blameworthy unintentional killings are involuntary manslaughter.