Den·ver boot 
/ˈdɛnvɚ-/ noun
plural ∼ boots /ˈdɛnvɚ-/ noun [count] US : an object that the police lock onto one of the wheels of a car so that the car cannot be moved ◊A Denver boot is usually placed on a car in order to force the car's owner to pay money that is owed for parking illegally. —called also (US) boot (Brit) clamp (Brit) wheel clamp
