The U6 unemployment rate counts not only people without work seeking full-time employment (the more familiar U-3 rate), but also counts "marginally attached workers and those working part-time for economic reasons." Note that some of these part-time workers counted as employed by U-3 could be working as little as an hour a week. And the "marginally attached workers" include those who have gotten discouraged and stopped looking, but still want to work. The age considered for this calculation is 16 years and over
Well I must be more out of it than I thought, because this is the first time in my 59 years that I’ve heard of the unemployment referred to by the terms U3 and U6.