On Vox: Word of the Day.

GRANDFATHER CLAUSE, n.

An exception that allows an old rule to continue to apply to some existing situations, when a new rule will apply to all future situations. It is often used as a verb: to grandfather means to grant such an exemption. (e.g. a “grandfathered power plant” might be exempt from new, more restrictive pollution laws).

Originally posted on wildernesscat.vox.com