RICO is often used to try to prove that a legal business was being used for illegal means, and, at its inception, was used to prosecute drug traffickers or organized crime members.
But in recent years prosecutors have applied RICO to government officials accused of using their offices for personal gain---for example the 28 various former and current Atlanta public school officials who recently went to jail.
There are federal RICO's and state RICO's. To bring a case under state RICO law, there must be at least two underlying felonies such as fraud, bribery, witness tampering (among others).
RICO gives prosecutors latitude to include multiple defendants charged with various crimes in the self-same indictment, and to charge that they were allegedly part of an ongoing criminal enterprise.