This is what persons not in labor force means as a technical category for the BLS:
Persons who are neither employed nor unemployed are not in the labor force. This category includes retired persons, students, those taking care of children or other family members, and others who are neither working nor seeking work. Information is collected on their desire for and availability for work, job search activity in the prior year, and reasons for not currently searching.
http://www.bls.gov/cps/lfcharacteristics.htm#nlf
Why would you come here and lie? Or do you just not know what you're talking about?
For those who want a closer look at these numbers
as the BLS supplied them, and not the interpreted graph in the OP's link, here you go:
http://www.bls.gov/news.release/empsit.t16.htm
Of course baby boomer retirement has to be factored into the comparison of the percentage to 1979. As was noted by an actual, y'know, economist last August the last time people had a fit about this:
"We have consistently held the view that the labor force participation rate would not rebound any time soon and its decline is mainly driven by the ageing (sic) of the population and the exit of the baby boomers from the labor market," Barclays Capital economist Michael Gapen wrote in a research note. "Therefore, the decline in the unemployment rate is not reflective of underlying strength in employment in this report."
The number of Americans the BLS says are "not in the labor force" has risen by 2.7 million in the past year, to 88.9 million. That sounds bad -- nearly three million people dropping out of the job market.
But of that 88.9 million, just a little less than 7 million people who are out of the labor force say they still want a job. That is a horribly high number. But it has only grown by 488,000 in the past year. In other words, of the 2.7 million people who have dropped out of the labor force in the past year, about 2.2 million of them say they're not interested in finding a job anyway.
And what are the majority of these 2.2 million people who don't want a job doing instead? Retiring, it seems. About 1.6 million people who have dropped out of the labor force in the past year are 65 and over, according to the BLS.
http://www.huffingtonpost.com/mark-gongloff/labor-force-participation-rate_b_1865027.html