Prototyping stage of an R&D process. This stage is about making something tangible, in the physical world, that uses a design and that works to a satisfactory level.
During the R&D process there is a cycle between Prototyping and Design, meaning that the prototyping process might unravel problems with the design, which will trigger changes of the design.
Prototyping produces a detailed description of a tangible thing, how it is made, how it functions, how well it functions. This description is based on empirical data or physical experimentation.

This process is also known as Testing and Refinement: Construction and evaluation of multiple pre production versions of the product. Early (alpha) prototypes are usually built with production intent-parts-same geometry and material properties as intended for the production version of the product but not necessarily fabricated with the actual processes to be used in production. Alpha prototypes are tested to determine whether the product will work as designed and whether the product will satisfy the key customer needs. Later (beta) prototypes are usually built with parts supplied by the intended production process. Beta prototypes are extensively evaluated internally and are also typically tested by customer in their own use environment. The goal here is to answer questions about performance and reliability in order to identify necessary engineering changes for the final product.

INPUT: a product design
OUTPUT: a detailed description placed in the main document

More than one prototype can be made, tested and documented during this process.