If you have typed jury def into a search box, you are looking for a short, clear definition, and here it is: a jury is a group of ordinary citizens, chosen at random from the community, who are asked to hear evidence in a legal case and decide on the facts. In a criminal trial, the jury decides whether the defendant is guilty or not guilty. In a civil trial, the jury decides whether one side is liable and, if so, what compensation is owed. This guide gives the full jury def in plain English, explains the different kinds of jury, and answers the questions people most often ask about jury service.
The jury system is one of the oldest features of English-speaking legal systems, and it rests on a simple idea: that important decisions about guilt, liability, and punishment should not be left to a single official, but should be made by a cross-section of the community. That idea travelled from England to the United States, Canada, Australia, and many other countries, and it remains a cornerstone of fair-trial rights today. For more on how courts handle cases day to day, see our guides to court disposition meaning, live court TV, and live trials on Court TV.
Jury Def: The Short Answer
The simplest jury def is this: a jury is a panel of citizens sworn to decide the facts of a case impartially, based only on the evidence presented in court. Jurors are not lawyers and are not expected to know the law in advance. The judge explains the relevant law, the lawyers present evidence and arguments, and the jurors weigh that evidence, judge the credibility of witnesses, and reach a verdict. Jurors do not decide what the law should be; they decide what happened, and then apply the judge’s legal instructions to those facts.
Two principles sit behind that definition. The first is impartiality: jurors must not have a personal interest in the case, must not have made up their minds before hearing the evidence, and must not discuss the case with outsiders or research it independently while the trial is running. The second is collective judgement: a verdict is the decision of the group, reached through deliberation, not the opinion of any single juror. Those two principles explain most of the rules that surround jury service, from the selection process to the secrecy of the deliberation room.
Jury Def Explained: Grand Jury vs Trial Jury
The most important distinction in any jury def is between the two main kinds of jury. A trial jury, sometimes called a petit jury, is the jury most people picture: a small group, usually six to twelve members, that hears a trial and delivers a verdict. A grand jury is different. It does not decide guilt or innocence. Instead, it reviews evidence presented by a prosecutor and decides whether there is enough evidence to bring criminal charges at all. Grand juries are larger, often sixteen to twenty-three members, and their proceedings are held in private.
| Feature | Trial jury (petit jury) | Grand jury |
|---|---|---|
| Purpose | Decide guilt, liability, or compensation at trial | Decide whether charges should be brought |
| Size | Usually 6–12 members | Usually 16–23 members |
| Proceedings | Public trial, both sides present evidence | Private; usually only the prosecution presents |
| Outcome | Verdict: guilty or not guilty, liable or not liable | Indictment (charges proceed) or no bill (charges dropped) |
| Duration | Days to weeks, for one case | Weeks to months, hearing many cases |
There are also specialist variations. A coroner’s jury, in some jurisdictions, helps determine the cause of an unexplained death. A hung jury is not a type of jury at all, but a situation: it describes a trial jury that cannot agree on a verdict, which usually leads to a mistrial and may lead to a retrial. Understanding these distinctions makes the basic jury def much more useful, because news reports often mention grand juries and trial juries without explaining which one they mean.
Jury Def: How Jurors Are Chosen
Jurors are normally selected at random from lists such as electoral rolls or driving licence records, and people summoned for jury service receive a formal notice telling them when and where to attend. On arrival, potential jurors go through a selection process known in the United States as voir dire, from a French phrase meaning “to speak the truth”. During voir dire, the judge and the lawyers ask questions to check whether a potential juror can be impartial. Someone who knows a party in the case, has already formed a strong opinion, or has a conflict of interest can be excused.
Lawyers can also remove a limited number of potential jurors without giving a reason, using what are called peremptory challenges, although these cannot be used to discriminate on grounds such as race or sex. The aim of the whole process is a jury that reflects the community while being free of bias in the particular case. Once selected, jurors take an oath or affirmation promising to decide the case honestly and on the evidence alone.
Not everyone is eligible. Rules vary by country, but common disqualifications include being below the minimum age, having certain serious criminal convictions, or having a mental-health condition that prevents a person from serving effectively. Some professions, such as serving police officers or judges, may also be excluded, because their work could compromise impartiality. Most jurisdictions also allow people to defer service for genuine hardship, such as serious illness or caring responsibilities, though outright exemptions are narrower than many people expect.
Jury Def: Deliberation, Verdicts, and Unanimity
After both sides have presented their cases, the judge instructs the jury on the law, and the jurors retire to a private room to deliberate. Deliberation is the heart of the jury system: jurors discuss the evidence, test each other’s reasoning, and work towards a verdict. They elect a foreperson to lead the discussion and to announce the verdict in court. Jurors may ask the judge questions during deliberation, for example by requesting that a piece of evidence be shown again or that a legal instruction be clarified.
The standard of proof differs between criminal and civil cases, and this is a crucial part of any full jury def. In a criminal trial, the prosecution must prove guilt “beyond reasonable doubt”, a high bar that reflects the seriousness of a conviction. In a civil trial, the standard is usually “on the balance of probabilities”, meaning that something is more likely than not. That difference explains why the same facts can lead to different outcomes in criminal and civil proceedings arising from the same events.
Whether a verdict must be unanimous also varies. Many criminal systems require unanimity, or allow a majority verdict only after the jury has deliberated for a long time without agreement. In some civil cases, a majority verdict is enough from the start. If a jury cannot agree at all, it is called a hung jury, the judge declares a mistrial, and the prosecution or claimant must decide whether to retry the case. A not-guilty verdict in a criminal trial is final in most systems: the defendant cannot be retried for the same offence except in narrow, exceptional circumstances.
Jury Def: What Jury Duty Actually Involves
For most people, the jury def they care about is practical: what happens if I am called? The short answer is that you attend court on the date given, bring the summons and identification, and wait to be assigned to a trial. Trials can last a day or several weeks, and jurors are usually told the expected length before selection. Employers are generally required to allow time off for jury service, and jurors receive a modest allowance for expenses and, in some systems, for lost earnings, though the amount rarely matches a full salary.
During the trial, jurors must follow strict rules. They must not discuss the case with anyone outside the jury, must not read news coverage of the trial, must not research the case online, and must not visit any location connected to it. These rules exist to protect impartiality: a verdict must rest on the evidence heard in court, not on rumour or outside information. Breaking them can lead to a juror being dismissed, a trial being abandoned, or, in serious cases, contempt of court proceedings. After the verdict, jurors are usually free to discuss their service, though some jurisdictions restrict discussion of deliberations specifically.
Many people find jury service demanding but rewarding. It is one of the few occasions when ordinary citizens exercise direct power over the legal system, and jurors often report that the experience changed how they think about justice. It is also, for most people, a once-in-a-lifetime civic duty: once you have served, you are usually exempt from being called again for several years.
Jury Def: Frequently Asked Questions
What is the simple jury def?
A jury is a group of citizens chosen to hear evidence in a legal case and decide the facts, delivering a verdict of guilty or not guilty in a criminal trial, or a finding of liability in a civil trial.
What is the difference between a jury and a judge?
The judge decides questions of law and manages the trial, while the jury decides questions of fact. In trials without a jury, the judge decides both, which is known as a bench trial.
How many people are on a jury?
It depends on the jurisdiction and the type of case. Trial juries usually have six to twelve members, while grand juries usually have sixteen to twenty-three members.
What happens if a jury cannot agree?
The jury is described as hung, the judge declares a mistrial, and the case may be retried with a new jury.
Can I refuse jury service?
You generally cannot refuse without a valid reason, but you can ask for a deferral or excusal for hardship, illness, or ineligibility. Ignoring a summons can lead to a fine.
Conclusion
The jury def, at its simplest, is a group of ordinary people trusted to decide the facts of a case fairly and impartially. Behind that simple definition sits a system of selection, deliberation, and safeguards that has been refined over centuries, from the grand jury’s gatekeeping role to the trial jury’s verdict. Whether you are preparing for jury service, studying law, or simply trying to understand a news report, knowing the difference between jury types, the standards of proof, and the rules jurors must follow turns a one-line definition into genuine understanding. And that understanding is the point of the system itself: justice decided not by officials alone, but by the community.