chambers, in law, the private offices of a judge or a judicial officer where he hears motions, signs papers, and deals with other official matters when not in a session of court.

Chambers are the private rooms where judges may hear matters, transact business, or have legal discussions with lawyers in private, it is usually used in the plural in this sense. If a trial is “in chambers,” it means that the trial happens in a courtroom without the public, newspaper reporters, etc.