To contest is to challenge an assertion made in a court of law. For example, a defendant may contest charges made against them. An attorney may contest a claim made by a witness on the stand. People contest positions or statements made in court when they disagree with them, and when they believe that there is good cause for argument on the matter
When a person contests something in a court of law, they are basically saying that they would like to argue the point. Contesting is central to the basic function of trials because it allows one party to disagree with another. It allows dialogues to take place to resolve the matter. Defendants can also choose not to contest something. For example, if a defendant wishes not to disagree with charges made against them,then they can enter a plea of "no contest." Although different than a direct admission of guilt, a plea of no contest means that the defendant is not denying that they are guilty. Pleas of no contest can result in a lesser sentence. That is why they can be appealing to certain defendants.