Some call them HENRY's—High Earners Not Yet Rich. Others call them the Faux Riche—people who look rich but aren't.
In my last book, I called them the High-Beta Rich, a new class of wealthy whose spending and wealth fluctuate wildly with markets.
A new paper calls them the "hand-to-mouth" wealthy. And it says there are 70 million such households in the U.S., suggesting that wealth today is far more precarious than many think.
The paper, by economists Greg Kaplan, Giovanni L. Violante, and Justin Weidner said these families often own homes, cars, and boats, but spend virtually all of their paychecks.
The high costs of college and other bills has made many wealthy families feel more vulnerable to economic shocks—especially when their wealth is tied up in illiquid assets.
(Read more: YUMMY's: Luxury's great hope)
"The wealthy 'hand-to-mouth' are households who hold little or no liquid wealth (cash, checking and savings accounts), despite owning sizable amounts of illiquid assets," the study said.
The paper said that when governments create stimulus programs, they target the poor. But they might do well to also target the hand-to-mouth wealthy, since they too are likely to spend the extra money and help the economy.