Русско-англо-русский юридический словарь

A legal district or judicial district denotes the territorial area for which a legal court (law) has jurisdiction. (Wikipedia)

In the federal system, the lowest court is the district court. There are 94 US federal judicial districts, with at least one district court in each state. (BBC News)

The 94 federal judicial districts are organized into 12 regional circuits, each of which has a court of appeals. (United States Courts)

The judges would literally travel in a circuit, bringing the court to various places in the region, hearing the relatively small number of appeals that would come to them. (Time)

Historically, in the U.S., state and federal court trial judges, for example, had to travel routinely to numerous locations in a specific geographical region to hear cases. People referred to the various locations with the region as a circuit; this is how the term circuit judge came about. Today a circuit judge is more likely to be assigned to just one courthouse. (PracticalAdultInsights)

The country is divided into 8 circuits for the purposes of the Circuit Court, which comprises the President of the Court and up to 45 ordinary judges. One Circuit Judge is assigned to each circuit, except in Dublin, where 10 judges may be assigned, and Cork, where there is provision for 3 judges. (citizensinformation.ie)