when a person intentionally kills another person after "adequate provocation"; that is, there has been action that was sufficient to incite an "ordinary person" to "sudden and intense passion" such that s/he loses self control. It should be noted that the time between provocation and the killing should not be long enough for the passion to have cooled off.
Involuntary manslaughter generally occurs in only two cases. The first is when someone is killed due to criminal negligence, and the second is when someone is killed during the commission of another crime, where the intent was not to cause bodily injury or death.
If it is a murder someone just killed someone on purpose and manslaughter is an accidental murder like a drunk driver hit someone head on and killed someone they're negligence from being drunk is what killed that person, it wasn't premeditated.
See if I can break it down in an understandable way...
There are several degrees of murder, but murder generally is classified as causing death to another with malice aforethought. Meaning that you planned and/or intended for your victim to die.
Manslaughter can be either voluntary or involuntary. Meaning that you took a life, but without forethought and intent. If you and I get into a fight and I pull my pocket knife out and in the struggle I catch you in the throat and you die...I did not mean to kill you, I did not plan to kill you...but due to my actions you are still dead, but I knew I wanted to hurt you, and the knife was capable of doing that... That is voluntary manslaughter.
Say me and me Grandfather go out into the woods and start peeling off some practice rounds. You are passing by unknown to us and you catch one of those bullets and die. We did not mean to kill you, and had no intention to kill you, but our reckless act still caused your death. That would be involuntary manslaughter.
Manslaughter. I did, or didn't do, something that caused someone to killed - like a stranger or a friend, - I had no intention of killing that person but it was indeed my hand that caused it.
Second-degree murder. I killed him or her, fer sher, but it was 'in the moment' - I caught my wife in bed with another man while I was cleaning my shotgun, and don't remember much else.
First-degree murder. I planned it - I needed the insurance money, and he/she was a gamblin', drinkin' piece of garbage - I hid in the shed until they came out and "bam" with pitchfork. Buried the body on the back forty.
Murder is said to be the unlawful killing of a human being with the intention of doing so while manslaughter is said to be the killing of a human being by an individual without the intention of committing the act.