Definition from Nolo’s Plain-English Law Dictionary

1) An official or employee who handles the business of a court or a system of courts, maintains files of each case, and issues routine documents. Almost every county has a clerk of the courts or county clerk who fulfills those functions, and most courtrooms have a clerk to keep records and assist the judge in the management of the court.
2) A young lawyer who helps a judge or a senior attorney research and draft documents.

Definition provided by Nolo’s Plain-English Law Dictionary.