According to financial experts at CNBC, a  healthy "off the books" economy is keeping the U.S. from economic disaster. Simply put, the underground economy is people doing lots of small, temporary jobs -- or even regular jobs that are paid with cash -- and not recorded in any ledgers.

CNBC defines it this way:

The shadow economy is a system composed of those who can't find a full-time or regular job. Workers turn to anything that pays them under the table, with no income reported and no taxes paid — especially with an uneven job picture.

According to CNBC, some 8 percent of the total U.S. gross domestic production is from this shadow economy. That number was at least 4 percent less five years ago! What was once confined to the lawn-care, agricultural and the food-service industry has now spread to even hi-tech fields.

For example, a business might pay a computer designer a few hundred dollars for some work under the table. Or a technology specialist might take on additional work on the side and it's done with a handshake and no W-2 or W-9 forms. Experts say every country has one, but the rapid growth of the U.S. underground economy is a sign that economic conditions have to change.

Why is this economy growing?  According to Fordham University Professor of Personal Finance Laura Gonzalez:

"There's a lot of uncertainly about immigration changes and who will be legal, and about paying for Obamacare. Most workers in the shadow economy are in the country illegally. Government rules are keeping businesses from hiring."

As more and more workers -- even skilled ones -- find it harder to find jobs, they turn to these so-called shadow jobs to survive. According to tax experts, the underground economy has also resulted in hundreds of millions of dollars in lost tax revenue to the government. Some even say tax rates would be lower if this shadow revenue were reported.

However, critics say if the underground money were reported, it still would not prevent irresponsible government spending. They say the government overspends regardless of how much revenue the economy is generating.

Experts also say the number of or U.S. citizens (especially skilled workers) entering this economy is exploding.