Some departments or agencies have an unit dedicated to
combatting organized crime. Examples would be departments like the
Federal Bureau of Investigation, New York Police Department, and so
forth.
Organized crime is exactly what it sounds like. Crime that is
executed in an organized fashion, or by an organized group. La Cosa
Nostra (Italian Mafia) is an example of an organized group that
commits crimes, thus they're under constant investigation by
Organized Crime Units.
Organized Crime can also be instituted into legal organizations
(any company ever), and may involve financial crimes like
embezzlement and money laundering.