A patent is an exclusive right granted to an inventor or the inventor’s successor in title, referred to as the patentee, for a period of time, typically 20 years from the date of application for the patent, but subject to annual payment of a renewal fee, usually from the third year after the application date until the date of expiration of the patent.  There are some exceptions to the above renewal rule, for example, in the USA where renewals are not paid annually but according to a different schedule until expiry thereof.