A jury is a sworn body of people convened to render an impartial verdict (a finding of fact on a question) officially submitted to them by a court, or to set a penalty or judgement. Modern juries tend to be found in courts to ascertain the guilt, or lack thereof, in a crime. In Anglophone jurisdictions, the verdict may be guilty, not guilty, or (in Scotland) not proven. Juries are composed of jurors (also sometimes known as jurymen), who are by definition layman finders of fact, not professionals.
The old institution of grand juries still exist in some places, particularly the United States, to investigate whether enough evidence of a crime exists to bring someone to trial.
The jury arrangement has evolved out of the earliest juries, which were found in early medieval England. Members were supposed to inform themselves of crimes and then of the details of the crimes. Their function was therefore closer to that of a grand jury than that of a jury in a trial.