Grand Jury (noun) – A large jury which investigates crimes and indicts defendants in felony cases. The grand jury is a jury of laypersons, who examine evidence to determine whether the evidence suggests probable cause to believe a person or entity accused of a crime has indeed committed it. If so, it authorizes an indictment against the defendant, which is the basis for arrest and trial before a different jury that determines guilt.
Sometimes the grand jury is strictly summoned to investigate a crime, but usually, it is summoned to consider bills of indictment, which its foreperson endorses to allow indictment or not. A refusal by a grand jury to issue an indictment does not amount to an acquittal, and jeopardy does not attach, so a prosecutor who fails in the first attempt at indictment is free to seek indictment from a later grand jury.