Like insurance to stave off financial disaster, an annuity is something you purchase to guarantee that you won’t run out of money if you live a long time. Such financial guarantees are attractive. After all, we don’t know how our investments will perform: This year may be the first in a while that your stock and bond index funds both lose money.

Still, annuities are not a mainstream product. This is partly the fault of the annuity companies, since they have long outsourced the sales process to people who do not always have customers’ best interests at heart. Word is out about how annuities are sometimes sold, and it’s not good.

Another problem: The annuity product lineup has become so filled with complex offerings trying to solve every problem and answer any objection that the word “annuity” itself can mean lots of different things. I’ll divide them into four categories.

Paycheck Annuities

Paycheck annuities are the simplest annuities, and they are kind of like a pension. You hand over a pile of money, and in exchange you can receive a regular check for life.

An immediate income annuity generally starts sending checks very soon, and they keep coming until you die. What you get each month will depend in large part on how much money you hand over, your age, your sex, whether you’re including a spouse in the package (so the checks keep coming until the second person dies) and the prevailing interest rates at the time you buy the annuity.

Deferred income annuities, also known as longevity insurance, work similarly, but the checks don’t start coming right away. The longer you wait to receive payments — you buy at 65 but don’t start collecting checks until 85, for example — the bigger the checks will be.

There is risk involved with a deferred income annuity. Each year that you wait in between the purchase and the first check brings you closer to death, and the annuity company is betting on your eventual demise. The fun — broadly speaking — in annuities is beating the odds and collecting checks until you’re 105.

Fixed Annuities

Fixed annuities start the same way: You hand over some money. That money grows for a predetermined period at a rate that is relatively easy to explain and understand (that’s the “fixed” part); then you can turn it into a regular check for life if you’d like.

Sometimes, the amount that the annuity company credits to your account will change once per year based on prevailing interest rates. Other times, in the case of multiyear guaranteed annuities, it works more like a certificate of deposit — you will know exactly how much money you’ll accumulate over time. These annuities tend to run longer than standard certificates of deposit.

Variable Annuities

Variable annuities exist for people who want to have their cake and eat it, too. They can offer a guaranteed check for life with a promise that they won’t lose money. But variable annuity buyers can get more money than the baseline minimum, depending on how certain mutual funds that they select perform.

The annuities I described above don’t give their owners access to the stock market. But variable annuities come with what are known as sub-accounts that can.

That access comes at a price, though. The fees here also tend to be so high that they have been the subject of many investor alerts from regulators over the years. My colleague Tara Siegel Bernard explained variable annuities in more detail in 2015.