It's the reverse of life insurance.
You pay the company a certain amount of money every month/year/whatever. When you retire, the company pays you back each month/year/whatever, some other amount based on what you paid in -- more than what you would have gotten with an ordinary investment, and you keep getting paid for life, regardless of how long you live. On the other hand, if you die early, the company keeps everything you've put in. It's a bit like Social Security, except private, and the company makes its profits off of people who don't live long enough to collect much.
What's this called, and why don't you hear much about it?