Confusing terms being used.
My definitions;
PDI (pre-delivery inspection) - performed by the service technician before the buyer arrives for delivery. This is called prep by a car dealer and is intended to verify correct operation of all systems and find glaring warranty issues.
Walk-thru - performed by a dealer representative (lot boy, salesman, or service tech) with the buyer to demonstrate operation of systems.
Another one could be PPI (pre-purchase inspection) - performed by buyer to find glaring omissions or warranty items.