Family of Scale Models/Prototypes
Built to demonstrate relations of adjacent parts.
Built to scale; need not work.
Built to illustrate the concept functioning -- especially the relative motions of connected moving parts.
Not always to full scale; probably does not operate optimally.
Built to demonstrate important design parameters; used to test reliability, speed, accuracy, etc.
Usually hand built; often full scale; durable to withstand testing.
Built to illustrate performance requirements met, production problems resolved, quality control achievable, etc.
Built as like the mass produced item as possible, differing only in the volume level of production.