Murder vs. Manslaughter
California Penal Code §187 specifically defines murder as the unlawful killing of a human being, or a fetus, with malice aforethought. This is similar to voluntary manslaughter as they both involve the intent to kill. However, murder requires malice, which is basically, a willful and wanton disregard for human life. There are occasions when a murder charge can be reduced to manslaughter, particularly by claiming "heat of passion" or "sudden quarrel."
As a comparison, California Penal Code section 192(b) defines involuntary manslaughter. When there is a death and you are accused of killing a person, but without malice, without intent to kill, and without the conscious disregard for human life, it falls into the involuntarily manslaughter classification.
Vehicular manslaughter is similar but applies to situation with a driver. In a driver operates the vehicle in an unlawful manner, with or without gross negligence, during the commission of a lawful act which may produce death, they can be charged with vehicular manslaughter.