A rider, or rider-roll, signifles a schedule or small piece of parchment annexed to some part of a roll or record. It is frequently familiarly used for any kind of a schedule or writing annexed to a document which cannot well be Incorporated in the body of such document. Thus, in passing bills through a legislature, when a new clause is added after the bill has passed through committee, such new clause is termed a “rider.”
RIDER
TheLaw.com Law Dictionary & Black's Law Dictionary 2nd Ed.