Grandfather. If you look at the website, it explains in detail:

A “grandfather” clause, “grandfather” policy or “grandfathering” in IT s a provision in which an old rule continues to apply to some existing situations while a new rule will apply to all future cases. Those exempt from the new rule are said to have grandfather rights, acquired rights, or to have been grandfathered in.

Why it’s problematic:

“Grandfathering” or “grandfather clause” was used as a way to exempt some people from a change because of conditions that existed before the change (e.g., we’ve grandfathered some users on an unlimited data plan.”) “Grandfather clause” originated in the American South in the 1890s as a way to defy the 15th Amendment and prevent black Americans from voting.