Annuity refers to a financial product in which a fixed/variable sum of money is paid to an individual at regular intervals.
Most popularly, it is a type of contract between an individual and an insurance company, where the individual agrees to make a lump-sum or a series of payments, and in return, the company pays a fixed/variable amount of money to him/her regularly, beginning either immediately or at some future date.
The main goal of annuity is to provide a regular income stream to an individual, especially after his/her retirement.