Murder, rape, burglary. These are what we know today as crimes, but it was not always so. Back in Roman times these were simply offenses against the individual. It was not until later on in post-Roman Europe that concept of offenses against the social order emerged. These offenses are so serious that they are dealt with by separate laws. Criminal law.
If you commit an offense that harms society as a whole then you will be subject to the penalties determined by criminal law. If you commit an offense that harms only an individual then you will be subject to the penalties determined by civil law. Under criminal law a defendant is likely to face jail time, whereas under civil law a financial penalty is a more likely punishment.
For a crime to have been committed two conditions need to be present: the criminal must have had a criminal intent, and they have to have undertaken the act. Mens rea is the legal term for criminal intent, and actus reus is the legal term for having committed the act. There are some rare crimes that do not need these two conditions to be present, and these are crimes of strict liability. With these crimes it does not matter whether there was intent or not.
State statutes, case law and federal statutes are the three main ways that crimes are defined. Of these the most interesting is case law. Case law emerges from specific trials, where judges publish their rational for rulings. These opinions serve as precedents for future cases. However, exactly what constitutes a crime is sufficiently broad for defense lawyers to make arguments case by case.
There are a number of elements that make up a criminal offense, and in the US criminal justice system the main thing that is debated in the trial courtrooms nationwide is whether each of these elements was present. This holds true whether the trial is in the state courts, federal courts, or special state criminal courts