A district court may grant each side in a civil or criminal trial the right to exclude a certain number of prospective jurors without cause or giving a reason.
Source: U.S. Courts
A challenge to a potential juror in a case, by either the defense attorney or the prosecuting attorney, that usually results in that person's disqualification from service on the jury and does not require either attorney to say why the challenge is made. The law limits the number of peremptory challenges allowed. (Compare challenge for cause.)
Source: California Courts.