Judgment as a matter of law is when a court makes a trial ending decision that one party in a case does not have enough evidence to support its claims. After this judgment is made, there is no further testimony or evidence presented. The trial is simply over. Parties in a lawsuit may motion for a jugdment as a matter of law if they believe the other party has insufficient evidence.
Judgments as a matter of law are made when a court believes that the decision is so clear in favor of one party, that any reasonable jury would make the same decision. For example, the prosecution may motion for a judgment as a matter of law in an assault case if there is indisputable surveillance video footage that shows the defendant assaulting a victim. In this case, the judge may assume that any attempt by the defense to prove otherwise would be futile because any reasonable jury could clearly see the defendant committing the crime.