A clause that exempts certain people or businesses from new limitations or restrictions, thus allowing them to continue doing or benefiting from something as they did before. Originally referred to a clause added to the constitutions of some Southern US states that exempted people with relatives that had voted before 1867 from strict new voting requirements, in effect disproportionately limiting the ability of African Americans to vote. No, I still get to pay the reduced rate, thanks to a grandfather clause in my contract.