Prototypes or prototypical instances combine the most representative attributes of a category. It is the best exemplar among the members of a category and serves as a cognitive reference point with respect to which the surrounding "poorer" instances are categorized.
A prototype can also refer to a test machine, circuit or program which is designed for demonstration purposes. It also enables the testing of the new product's design before the product is put into production. Problems or deficencies in the products design can be discovered and corrected. When the prototype is sufficiently refined and meets the functionality, robustness, manufacturabilty and other design goals, the product is ready for production.
NOTE: see: Categorization, Semantics
Computer Science
In computer science, the declaration of a subroutine is sometimes described as a prototype.