In chambers refers to discussions or hearings that are held within the judge's office (their “chambers”), in the absence of the public. According to the US Supreme Court website, “an in-chambers opinion is written by an individual Justice to dispose of an application by a party for interim relief, e.g., for a stay of the judgment of the court below, for vacation of a stay, or for a temporary injunction.”
[Last updated in April of 2022 by the Wex Definitions Team]