Final answer:
A license granting exclusive rights to an inventor to sell a new product for a certain time is known as a patent, typically lasting for 20 years.
Step-by-step explanation:
A license that gives the inventor of a new product the exclusive right to sell it for a certain period of time is called a patent. A patent is a government rule that grants an inventor the exclusive legal right to make, use, or sell their invention for a limited time. This includes developing new technology and products without competition, fostering innovation and providing a significant incentive for research and development. Typically, this exclusive period, where a firm can earn monopoly profits, lasts for 20 years from the filing date of the patent application, after which the invention enters the public domain and can be freely used by others.