In some jurisdictions, murder is defined in terms of degrees. The term first-degree murder means a killer planned to kill a person with malice aforethought. In the United States and Canada, however, murder is always punishable by death. In England, murder does not have degrees. Rather, it is classified as a felony. In the United States, the punishment for murder carries a mandatory life sentence. In some countries, a defendant may be exempted from the sentence if he or she committed the crime while committing another serious felony.

In early common law, a suicide was considered murder, although the requirement that the person killed be someone other than the perpetrator precluded suicide from being a felony. Another defining element of murder is malice aforethought, or the deliberate killing of a person. In the past, the intent to kill someone must have been premeditated and there was an appreciable amount of time between the actual killing and the intention to commit it. However, in recent years, courts have liberalized the definition of a felony. While some jurisdictions still require the person to have actually premeditated the crime, the term can now be used for any of four states of mind.

The criminal definition of a felony is very broad, so it is essential to understand the differences between the federal and state laws. In many jurisdictions, the term means killing a human being. In some cases, a defendant may be charged with murder because he or she intentionally killed a person. In other cases, the crime may be categorized as manslaughter. In some jurisdictions, there is no legal definition for homicide, but it is generally assumed that a victim was murdered with intent.