By Scott Cohn, Jun. 25, 2015, CNBC

More than 9 million Americans are unemployed, according to the Labor Department, and many more are underemployed. Yet in a recent studyby CareerBuilder, more than half of the employers surveyed said they had open positions for which they could not find a qualified applicant. It's not that those workers don't exist somewhere, the experts say. It's just that they're not necessarily located near the employers who want to hire them.

Experts have a term for this mismatch between jobs and the people to fill them: the skills gap. And it's a big reason that the new prime battleground among America's Top States for Business—and every other state for that matter—is which state offers the best workforce.

But what makes a good workforce? Having plenty of available people is a start, but only a start.

"Beyond measuring labor supply and demand indicators, assessing a region's degree of skill-set specialization is critical in order to effectively scale operations to the desired headcount," wrote site-selection consultant Keith Gendreau of Cushman & Wakefield in the trade publication "Area Development" this year.

It's a long and fancy way of saying that you can't close the skills gap without ... well, skills.