A group of individuals selected and sworn in to serve as the finders of fact in a civil or criminal trial, or in the case of a grand jury, to decide whether the facts warrant an indictment of the defendant. blue-ribbon jury. A jury for which only highly educated individuals have been selected, because they will be dealing with technical subject matter. grand jury. A jury selected and sworn in by a prosecutor to determine whether to issue indictments. petit jury. A jury selected to decide the ...