Crime is a legal, not a moral, term. In the eyes of the law, a crime is any act that is a danger to the peace and order of society, and is punished as such. However, some crime, such as murder or robbery, may also be a violation of moral law. On the other hand, a crime may be merely the breaking of a rule that has little or no moral significance, such as parking for 35 minutes in a 30-minute zone. Crime differs from sin in that sin is a violation of religious law, not the law of nations or communities.

The body of law that defines crime and specifies its punishment is called criminal law.

A crime is a public wrong, against society, punished by the state after a criminal trial. There are many private wrongs, against individuals, which are settled by the payment of damages as determined in a civil trial. These private wrongs are called torts. Automobile accident injuries caused by carelessness are good examples of torts.

For an act to be a crime, the person committing it must have intended to commit a wrongful act. For this reason an insane or mentally retarded person ordinarily cannot commit a crime. He can, however, be ordered to undergo psychiatric care, if eventually pronounced cured, he will go free. Some states have adopted a verdict of "guilty but insane"; a person convicted under this verdict, if pronounced cured, is subject to imprisonment for the crime committed while he was considered insane. Most states, except in unusual circumstances, will not hold children under a certain age responsible for committing crimes.

The same act may be looked upon by society as a crime in one period of history, but not in another. In some of the American colonies, for example, it was a crime to work on Sunday. On the other hand, new varieties of crime sometimes arise, such as income-tax evasion, expense-account cheating, or computer fraud.