A demurrer is a response to a petition which asks that it be rejected. People can demur a specific allegation, contest evidence, or can issue a blanket statement condemning an entire indictment. This legal challenge is heard by a judge, who decides whether or not the demurrer should be granted, given the information presented in the document and the specifics of the case. Not all legal systems allow people to use this technique to challenge pleadings and those who do may only allow it in courts of a certain level.
In the case of a demurrer, which is usually entered by the defendant, the defendant is not disputing the facts as presented. However, the defendant is arguing that either there is insufficient evidence or no legal basis for a case. On these grounds, the demurrer asks that the issue in dispute be rejected. The judge will have to evaluate the information and decide on the basis of prevailing law and legal precedent, issuing a ruling in the court in response to the demurrer.
For example, someone might enter a demurrer in a civil case arguing that the plaintiff has no grounds to file a case. The judge can review the demurrer and the facts as they are known and determine that, given the information in the original filing, the case should indeed be rejected. The judge may also rule that the plaintiff can amend the original case to correct it so that it will be valid. Finally, the judge may determine that the demurrer is incorrect and that the case must proceed.
While defendants are usually the ones writing demurrers, it is also possible for such a document to be filed in response to a statement or claim made by the defendant. In this case, the defendant's claim is asked to be considered for rejection because it lacks evidence or doesn't meet a legal standard. The judge will consider the demurrer and then issue a judgment.
In regions where such documents cannot be filed, people are not without options when it comes to challenging material in court on the grounds of insufficient evidence or poor legal basis. There are various motions which can be filed in challenge and reviewed by a judge, in procedures similar to those involved in the pleading stage when one side writes a demurrer in order to challenge materials or claims brought to court by the other side.