Rider

The term "rider" in the context of law and legislative measures refers to the practice of introducing complex bills which enact ancillary laws or measures.

From Webster's Revised Unabridged Dictionary (1913) [web1913]:

Rider \Rid"er\, n.

...

4. An addition or amendment to a manuscript or other

document, which is attached on a separate piece of paper;

in legislative practice, an additional clause annexed to a

bill while in course of passage; something extra or

burdensome that is imposed.