It seems that you can't pick up an HR publication without reading something about the so-called "candidate shortage."
Key employee leaves: candidate shortage. Restaurant short on help: candidate shortage. Staffing company can't fill job order: candidate shortage.
And so on.
The reality is that no free market has a shortage of anything. The laws of supply and demand do not stop applying simply because we are dealing with people.
That key employee left because she got a salary hike of $10k and a shorter commute. That restaurant stays chronically short of help because they don't pay enough and the bartenders are constantly hitting on the waitresses. That staffing company can't fill its job orders because Joey, the branch manager they recruited from the restaurant down the street, has no clue how to find workers with the appropriate skills and spends half of his day playing World of Warcraft anyway.
None of this means there is a shortage.
Shortages do exist when forces external to the free market interfere with the laws of supply and demand. Minimum wage laws can prevent employers from hiring workers by artificially pricing the pay rate above that which makes sense for the employer. Socialists outlaw temporary staffing, creating an artificial shortage of both workers and jobs.
But in the U.S. employment market today, few (if any) of these external forces disrupt the marketplace. Instead, the term "candidate shortage" has become the cop-out way of describing ineffective recruitment and retention practices.