A more thorough explanation:

Definition: The fee that an inventor must pay to the U.S. Patent and Trademark Office before their patent application can be issued as a patent.

Example: John has invented a new type of solar panel and has filed a patent application with the U.S. Patent and Trademark Office. After the application is reviewed and approved, John must pay the issue fee before his patent can be granted.

Explanation: The issue fee is a necessary step in the patent application process. Once an application is approved, the inventor must pay the fee to officially receive their patent. Without paying the issue fee, the patent will not be granted.