Dictionary.net

During jury selection, an opportunity for a party to a lawsuit to dismiss or excuse a potential juror without having to give a valid reason, as would be the case when a juror is challenged for cause. Depending on court rules, each party typically gets to make from five to 15 peremptory challenges. Although parties may generally use their peremptory challenges as they see fit, the U.S. Constitution has been interpreted to prohibit their use to eliminate all jurors of a particular race or gender from a jury.

In criminal practice. A species of challenge which a prisoner is allowed to have against a certain number of jurors. without assigning anv cause. Lewis v. U. S