What isdouble jeapordy

Jeopardy-  an exposure that an accused or a defendant is subjected to when on a jury for a certain offense.

Double jeopardy is an act or a procedural defense that prohibits a defendant from being tried again on similar offense or charges following a legal conviction. If this issue is being raised by the other party, a defendant may have a peremptory plea of autrefois acquit, which means the accused has been acquitted of the same charges and for this reason, the accused can't be retried under the principle of double jeopardy.
In other words, double jeopardy is a second trial or prosecution of a defendant  for the same charges after conviction or acquittal.

Double jeopardy is the prosecution of a person twice for the same offense.