With regard to patents, ‘annuity fees’ means the fee paid by the patent holder to keep the patent in force. In some cases, annuity fee should be paid for pending applications also. Annuity fee is also known as "maintenance fee" or "renewal fee". Some patent laws do not mandate annuity fee.
In the U.S., all utility patents which issue from applications filed on or after December 12, 1980 are subject to maintenance fees.