Standard of proof is the level of proof that is supposed to be provided in a court case in order for a party to win.
In civil cases, the standard of proof is "clear and convincing," meaning that it should be very apparent that the defendant committed the act of civil wrongdoing. For criminal trials, the standard of proof is "beyond a reasonable doubt." This means that no one on the jury should be able to reasonably suspect that the defendant is innocent.
The standard of proof is very important for court cases because it can have a large impact on how jurors vote. For example, in a murder case, if every juror except one believes that the defendant has been proven guilty beyond a reasonable doubt, then the one remaining juror could vote not guilty because, in their opinion, the standard of proof hadn't been reached. This could potentially change the outcome of the verdict.