Jury is a body of people who are convened to participate in hearing and render a verdict that will be impartial. Today it happens more often when members of jury decide whether a person accused is guilty or not. People who take part in this sworn body are called jurors.
There is a notion - Grand Jury. It is rare nowadays but still possible to find in some states. They usually investigate whether there is enough evidence or not. If not, then a person can't be brought to trial. This system comes from medieval England At that time jurors's task was to inform each other of details of this or that crime and to understand if there is enough evidence. If we compare today's system with that one we will see that the same function performs Grand Jury today.
There are several types of jury. We will start with petit jury. Their primary job is to listen to evidence presented by a defendant and a petitioner; after that they have some time for deliberation and considering a verdict. Jurors who can't come up with a decision belong to hung jury. And there is Grand Jury which is larger than petite jury. As for the functions, they were discussed above.
And the last thing to be discussed is the following: Who is eligible for becoming a juror? Requirements vary from state to state, country to country. When talking about the US it should be said that a juror must be at least 18 years old, have good knowledge of the English language, serve as a public official, open-minded and take into account views of others.