Rider is a term subject to different definitions. A rider is an attachment to a document which supplements or changes it. It is commonly used in insurance policies to add coverage, such as additional coverage for an engagement ring not covered under the general terms of a homeowner's policy. In the context of lawmaking, it is an amendment tacked onto a bill which in mostly unrelated to the main purpose of the legislation, but is a tactic used to get the amendment passed if the main bill is favored for passage.
A rider may also be a passenger. Depending on whether the rider pays a fare or not, different standards of duty attach to the driver in determining liability after an accident.