[Natsu]

"# Part time employed for non-economic reasons: 18.184 million people. Non-economic reasons include school or training, retirement or Social Security limits on earnings, but also childcare problems and family or personal obligations."

I would assume those people would fall into that category, but I might be missing something.

[gojomo]

That category is those who are part-time employed due to these reasons. People who have no job at all because of these reasons – perhaps because they don't even want a part-time job – fall into the 100+ million people over 16 neither working nor seeking work.