A motion for mistrial is a formal request made by a party during a trial, seeking to have the trial declared invalid due to significant errors or irregularities that affect the fairness of the proceedings. This motion can arise from issues such as juror misconduct, inadmissible evidence being presented, or prejudicial statements made in court that could influence the jury's decision. The goal is to protect the integrity of the legal process and ensure that the rights of the parties involved are upheld.