A partial or complete trial which is found to be null and void and of no effect because of some irregularity.
The sudden end of trial before it would ordinarily end because of some reason which invalidates it.
Once a mistrial is declared, the situation is as if the trial had never occurred.
Some common reasons for a mistrial include a deadlocked jury, the death of a juror or a serious procedural and prejudicial mistake made at the trial which cannot be corrected.