A more thorough explanation:

A working model is a physical sample of an invention that is built for testing and displaying to potential buyers. It is also known as "actual reduction to practice." While it is not required for a patent, it can help the applicant to clarify the description and establish a date of invention in the event of an interference.

For example, if someone invents a new type of engine, they may build a working model of the engine to test its functionality and demonstrate it to potential investors or buyers. This working model can help them refine the design and prove that the invention actually works.

Another example could be a working model of a new type of prosthetic limb. The inventor could build a physical model to test its functionality and demonstrate it to potential users or medical professionals.

These examples illustrate how a working model can be used to test and demonstrate the functionality of an invention, which can be helpful in securing funding or patents.