Whether it's for your criminal law class or for that juicy detective novel you're writing, knowing the different definitions of murder is a key detail. Not only must you sort out the various degrees of murder, but you also need to understand the definitions of homicide, murder and manslaughter. To top it off, there's voluntary and involuntary manslaughter.
Murder vs. Manslaughter
The bare bones difference between murder and manslaughter is intent. When someone commits a murder, this implies they planned to commit the act before doing it, even if the planning was brief. For example, a man's wife knows he's cheating on her so she determines when the lovers will meet up again, purchases a gun and kills them both. Manslaughter, on the other hand, implies no intent or planning. In this case, the wife walks in on her husband and his lover and is so distraught she shoots them both with the gun she is carrying.
Degrees of Murder
Degrees of murder indicates the gravity of the crime. First degree is the most serious and is used for premeditated and malicious murder. The first example is first degree murder. Second degree murder implies some thought, but not long-term planning. In the example, if the wife saw the two lovers, went into the other room and grabbed a gun, then shot them, that is second degree murder. Third degree murder is defined as murder committed while doing a malicious or felonious act even if murder wasn't the intention. For example, the wife breaks into the lover's house to snoop around. While there, she's confronted and pushes the lover to get away. If the lover falls down the stairs and dies, this is third-degree murder.
Voluntary vs Involuntary Manslaughter
Voluntary manslaughter is when the person committing the homicide does so in the heat of passion and acted before her mood could simmer. The example where the wife already has a gun on hand -- we'll assume she's a police officer and carries a gun on a regular basis -- and shoots the two lovers is voluntary manslaughter. Involuntary manslaughter is manslaughter without intention. For example, the husband and wife argue while she is driving. She runs a red light and her husband dies in the crash.
Third Degree vs. Involuntary Manslaughter
The line between third degree murder and involuntary manslaughter is thin. Both refer to causing a death without forethought. However, the key difference is that third degree murder is committed during or as a result of an act that is intentionally malicious. Involuntary manslaughter indicates that death was caused through an accidental act. That act may be illegal such as running a red light, but the act that resulted in the death was not done maliciously or intentionally.