First-degree murder is both the intentional and premeditated killing of a person, or as it is sometimes referred to with malice aforethought, which means the killer deliberately killed out of ill will toward the victim.
Second-degree murder is charged when the killing was intentional but not premeditated, but also was not done in the "heat of passion." Second-degree murder can also be charged when someone is killed as a result of reckless conduct without concern for human life.
Most states also provide for charges to be filed under the "felony murder rule." That means if someone is killed during the commission of another crime, such as bank robbery, everyone involved in the robbery can be charged with that murder, including the getaway driver who was not even inside the bank.