A demo car is one that's been used extensively by a dealership for test drives.
A program car is a car which has been used by an auto executive for typically one year or less, and then sold as a new car. Program cars are also known as finance or factory cars. (http://www.edmunds.com/advice/buying/ar
But some people consider program cars ones that have been in car rental fleets. Others consider lease returns (or sometimes just corporate lease returns) to be program cars.
They are all "used" cars even though some state laws may technically consider a program car or a demo a "new" car for registration purposes.
A car driven by a dealer executive for a year may have received better treatment than a rental or demonstrator car, but the executive may have loaned the car out to her 16 year old every weekend!