Challenge
A challenge is a request to remove a juror from the jury pool. It happens during the jury selection (voir dire) process of a trial. A challenge is raised either because of juror bias or interest in the case (challenge for cause) or simply because of a belief that a juror may not be receptive to that party's arguments (peremptory challenge). In selecting a jury, each party is allowed unlimited challenges for cause and a limited amount of peremptory challenges.
See also, Challenge for Cause, Peremptory Challenge.