A more thorough explanation:

The law of the trial is a legal principle or court decision that is not opposed and is used or relied upon during a trial. This means that if neither party objects to a certain legal theory or ruling, it becomes the law that applies to the case.

For example, if a judge gives a jury instruction and neither the prosecution nor the defense objects to it, that instruction becomes the law of the trial. This means that the jury must follow that instruction when making their decision.

Another example could be a court ruling on the admissibility of evidence. If neither party objects to the ruling, it becomes the law of the trial and the evidence is either allowed or excluded based on that ruling.

The law of the trial is important because it helps ensure that both parties have a fair and equal opportunity to present their case. If a legal theory or ruling is not objected to, it is assumed that both parties agree with it and it becomes the law that applies to the case.