A more thorough explanation:

A police court is a type of court that deals with minor criminal offenses. It may also hold hearings for more serious criminal cases to determine if there is enough evidence to send the case to a higher court for trial.

For example, in California in the early 20th century, a police court in Stockton had jurisdiction over "all misdemeanors punishable by fine or by imprisonment...all actions for the recovery of any fines, penalties or forfeitures prescribed for the breach of any ordinance of the city, of all actions founded upon any obligation or liability created by any ordinance, and of all prosecutions for any violation of any ordinance...[and] all civil cases, concurrently with the justices' courts of all actions and proceedings arising within the corporate limits of the city and which might be tried in such justices' court."

This means that the police court in Stockton had the power to handle minor criminal offenses, such as traffic violations or disorderly conduct, as well as civil cases within the city limits.

However, police courts are now virtually non-existent, and their roles have been taken over by municipal courts or trial courts.