grandfather clause

Definition from Nolo’s Plain-English Law Dictionary

1) A provision in a new law that limits its application to individuals or businesses that are new to the system, while those already in the system are exempt from the new regulation. For example, when Washington, DC, raised its drinking age from 18 to 21, people between those ages, who could drink under the old law, were allowed to retain the right to legally consume alcohol under a grandfather clause. 2) A provision of several Southern states' constitutions in the late 1800s designed to to keep blacks from voting; now unconstitutional, these grandfather clauses denied the vote to people who were illiterate or did not own property, unless their descendants had voted before 1867.

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