A prototype is the original model, a sample on which to base future designs. A company designing a new toaster will first design and build a prototype and then test it out and see if it's any good.
A prototype is your test case and becomes the model on which to base the design of the finished product. Often, however, the prototype can be a phase to work out the bugs. The prototype of our hands-free toothbrush was too dangerous; it needed to return to the lab for serious improvements. Like the word archetype, the word prototype can also mean the standard on which to base a definition of something. "A prototypical cheerleader is the girl to which all other cheerleaders might aspire."