Double jeopardy refers to a legal right of a person to not be put on trial twice for the same offense committed. If a person is already put to court for a certain crime, he/she cannot be prosecuted again in another court or the same court for the same crime as stipulated by the double jeopardy feature of the US Bill of Rights. Under the Fifth Amendment clause of this particular bill, defendants or those who committed crimes are protected from double prosecution or double jeopardy as many people refer to it. Double jeopardy as a legal right or defense in court is also applied by law in various countries with similar protection on double trial or prosecution.
In the US, the Bill of Rights specifically states three cases wherein defendants are protected under the double jeopardy law. The first case is when the defendant is already acquitted of his/her crime. In this particular case, no other trial can commence for the same offense because of the acquittal. In the same way, the opposite case of having been convicted of a crime is also part of the protection under double jeopardy. If a person was already declared guilty of a crime by one court for example, he/she cannot be tried again for the same crime. Under the double jeopardy law, people who have committed crimes are also given protection against multiple sentencing for a single crime. In the case of a person who was already convicted of murder, he/she cannot be tried again for manslaughter for the same crime. The defendant involved is also protected in terms multiple punishment for the same crime.
As with many laws and rules, the law concerning double jeopardy also has its exemptions. In the US for example, retrials for the same crime may be exempted from the protection of double jeopardy if the case is handled by another entity. If a particular case has been declared a mistrial, the rule on double jeopardy also does not apply.