There are two different types of courts that you might hear about if you are facing a criminal justice case. Even though they share the designation of being a jury, they are very different. In fact, one of these juries is one that you will likely never stand before.
The grand jury is a larger jury that meets before a criminal charge is levied against a person. This one consists of 16 to 23 people. The defendant typically doesn't appear before this jury, and neither does that person's legal representative.
When the grand jury meets, the members consider the evidence in the case to determine if there is probable cause in the matter. If there is, the grand jury recommends that an indictment is issued in the case.
The second type of jury is the trial jury. This is a smaller jury with six to 12 members. These individuals hear the arguments from both sides of a case to determine whether the defendant is guilty or not guilty. The deliberations about the matter are held in private; however, the trial itself is usually open to the public.
One primary difference between the two types of juries is that the court system is bound by the decision of the trial jury, but not the grand jury. Even if the grand jury finds that there is probable cause in a case, the prosecutor doesn't have to levy the charges. On the other side, the prosecution can opt to charge a person even if the grand jury doesn't find that there is probable cause.
Source: United States Courts, "Types of Juries," accessed Jan. 17, 2018