Murder is an unlawful homicide, the unlawful killing of one human being by another with malice aforethought. Malice for murder may be an express intent to kill or implied by intent to cause Great Bodily Injury, intent to commit an inherently dangerous felony (felony murder rule), or intent to commit an act with awareness of and conscious disregard for the unjustified risk posed to human life (Depraved Heart Murder).
At Common Law, there were no degrees of murder. Modernly, murder is in the first degree if it is an intentional, willful, deleberate, pre-meditated killing of another human being with expressed malice aforethought. Second Degree Murder is the unlawful killing of another human being with malice aforethought, express or implied, but without deliberation or premeditation.
Voluntary manslaughter is the intentional killing of another human being without malice aforethought, in the heat of blood, produced by adequate provocation. Provocation does not reduce a homicide to manslaughter; (a) if the blood had actually cooled at the time the blow was given, or (b) if there was a reasonable time for cooling. The provocation must be so great as reasonably to excite passion on an ordinary man and cause him to act rashly and without reflection.
Involuntary Manslaughter is the unlawful killing of another human being without malice and without an intent to kill, as the result of criminal negligence. This may be during the commission of an unlawful act not amounting to a felony or in the commission of a lawful act with might produce death in an unlawful manner.