Define indictment. Define information. Is a grand jury always required? If not, when is an indictment or an information used?

An indictment is a charge or written accusation, issued by a grand jury, stating that probable cause exists to believe that a named person has committed a crime for which he or she should stand trial. The indictment is filed with the trial court and becomes the formal charge against the defendant.
An information is a formal criminal charge, usually issued by a prosecuting attorney, against a criminal suspect. It is issued after a preliminary hearing before a magistrate, if the magistrate finds sufficient evidence to establish probable cause.
The federal government and about one-half of the states require a grand jury to make the decision as to whether the case should go to trial in felony cases. Thus, an information would be used in those states and those cases not requiring a grand jury.