A more thorough explanation:

The likelihood-of-success-on-the-merits test is a rule in civil procedure that requires a party seeking a preliminary injunction or trying to prevent the effects of a judgment during an appeal to demonstrate a reasonable probability of success in the litigation or appeal.

Let's say a company is suing another company for patent infringement. The plaintiff company wants to prevent the defendant company from selling the allegedly infringing product while the case is ongoing. To do so, the plaintiff company must show a likelihood of success on the merits of the case. This means that the plaintiff company must demonstrate that it is likely to win the case and that the defendant company is indeed infringing on its patent.

Another example could be a defendant who has been found guilty of a crime and is appealing the decision. If the defendant wants to avoid being sent to jail while the appeal is ongoing, they must show a likelihood of success on the merits of the appeal. This means that the defendant must demonstrate that there is a reasonable probability that the appeal will be successful and that they will not have to serve their sentence.

These examples illustrate how the likelihood-of-success-on-the-merits test is used in civil procedure to determine whether a party is entitled to a preliminary injunction or to prevent the effects of a judgment during an appeal. It ensures that parties do not use these measures frivolously and that there is a reasonable chance of success in the underlying case or appeal.