reverse insurance?

I have heard some describe an annuity as "the opposite of life insurance", what do people mean by that?

A good comment and point. Life insurance provides protection (a hedge) against the risk of dying too young. For example, a young parent might buy term life insurance to provide her family with a lump sum that equals several years of her annual income. The life insurance would replace lost income and provide for the family in the event of an early death.

An annuity is "the opposite" of life insurance in that it--among other things--provides protection against the risk of living too long. The risk of living too long--also referred to as longevity risk--may seem counterintuitive, but when retirement finances are involved the risk of outliving one's assets is very real. One of the most important benefits of an annuity is the promise of guaranteed income that will last as long as the annuity owner lives.

People are living longer and this trend will likely continue to increase. Unfortunately, the assets that most people have to fund retirement are not moving in the same direction as average lifespan. Annuities provide protection against this mismatch.