As far as euphemisms go, this one's a doozy.
Preneed customers are those who buy the services of a company before they actually have any use for them. It happens all the time in various industries, but the industry the term is most heavily associated with and that with a big enough segment of their business being associated with it so as to warrant a special heading in their ledgers, is the funereal services industry - preneed customers are those who buy cemetery plots, headstones, even book mortuary services like hearses and the like, before they're actually dead.
It sounds like a joke, but it's a big deal - the American Association of Retired Persons (a source I hope never to have to cite ever again) claims for there to be over 25 billion dollars tied up in preneed arrangements, and though the article doesn't explicitly say, I'm guessing that's in the United States alone. Preneed services can be in the form of preplanned or prepaid arrangements, the former consisting mostly of leafing through brochures on lonely sunday afternoons, the latter involving money placed into funds and/or annuities to be released upon death. Some insurance companies offer special plans to cover preneed services.
The problem with such arrangements (other than the necessity for their existence at all) is the weight brought to bear in recent years by funereal services conglomerates and, believe it or not, though it makes sense if you think about it, franchises. Much like the Wal-Marts of the dead and dying, these businesses, rather than taking the business that walks through their doors and making arrangements on a case-by-case basis, actively solicit the elderly to enter into legal arrangements out of (to paraphrase one of their daytime television spots from memory) the fear of being a burden.
It's also worth noting that this particular aspect of the business world is so relatively new and has grown so fast that it's less regulated than similar industries, and while the terms of any financial transaction of this nature are technically covered by the FTC, this particular type of arrangement is made inherently more complicated by the contract holder being, you know, dead. Many people entering into such agreements are doing so because of a lack of family to shoulder the organizational or financial burden, and If the funds are mishandled by their solicitors...
It's a shady business. Be wary.
Most statistical data taken from: