An annuity is an insurance product you can purchase to receive scheduled payment(s) in the future. They are often used to provide regular income payments during retirement, until death.
An annuity may be purchased with one lump sum payment or a series of payments in what’s called the “accumulation phase.” The insurance company will invest this money and provide one or more payments in the future, in the so called “payout phase.” Annuities can be useful in many scenarios, but there are ripoffs out there.
Investopedia’s guide to annuities
SEC article about annuities