A Denver boot on a parked car.
Denver boot definition by Webster's New World
Webster's New World College Dictionary Copyright © 2010 by Wiley Publishing, Inc., Cleveland, Ohio. Used by arrangement with John Wiley & Sons, Inc.
a large metal clamp locked to a wheel of a motor vehicle by the police to immobilize the vehicle: used primarily to force people to pay their parking tickets
Origin: after Denver
Denver boot definition by American Heritage Dictionary
A device locked to the wheel of a parked vehicle to keep it from being driven, used especially to force settlement of outstanding traffic violations.
Origin: After Denver, one of the first cities to use it.