When one or both parties to a legal action ask the judge to end the proceedings before the trial concludes, they are said to be moving for dismissal. A judge has the authority to dismiss a case in both civil and criminal proceedings, but may also deny such a motion. A dismissal may apply to an entire court case, or any cause of action thereof.
Either the plaintiff/prosecution or the defendant may ask for a dismissal. The judge may also dismiss the case him/herself, if s/he believes or finds evidence that the case has no validity, if one or both parties have tampered with or fabricated evidence, a statute of limitations has expired, or if the claim does not offer an appropriate legal remedy for the particular issue.
If a judge dismisses a case or grants such a motion on the part of the litigants, no evidence from either side is heard or examined. In the case of a civil action, the judge may dismiss the case without prejudice, which allows the suit to be filed again at some future date. When this happens, it is because the plaintiff and defendant have reached some kind of settlement. By dismissing without prejudice, the judge makes it possible for the plaintiff to bring the suit again if the defendant reneges (fails to honor or follow through) on the terms of the settlement.
On the other hand, if a case is dismissed with prejudice, the case is effectively terminated, and may not be filed a second time. Because of doctrine of double jeopardy, a criminal trial that has been dismissed is always "with prejudice," although that is not the legal terminology. In these cases, the prosecution may be able to charge the defendant with a separate crime. This happens only on rare occasions, however.