An indexed annuity is a deferred annuity whose return is tied to the performance of a particular equity market index.
Your investment principal is usually protected against severe market downturns, in that you may have an annual return of 0% but not less than 0%.
However, earnings are generally capped at a fixed percentage, so any index gains that are above the cap are not reflected in your annual return.
Indexed annuity contracts generally require you to commit your assets for a particular term, such as 5, 10, or 15 years. Some but not all contracts limit your participation rate, which means that only a percentage of your premium has a potential to earn a rate higher than a guaranteed rate.