As per Wikipedia: defines a current rider.
Rider (legislation)
In legislative procedure, a rider is an additional provision added to a bill or other measure under the consideration by a legislature, having little connection with the subject matter of the bill.[1] Riders are usually created as a tactic to pass a controversial provision that would not pass as its own bill. Occasionally, a controversial provision is attached to a bill not to be passed itself but to prevent the bill from being passed (in which case it is called a wrecking amendment or poison pill).
http://en.wikipedia.org/wiki/Rider_(legislation)