https://www.thebalance.com/what-is-the-real-unemployment-rate-3306198
In the widely reported unemployment rate (U-3), the BLS only counts those who have looked for a job in the past four weeks as unemployed. They're included in the labor force because their jobless situation is only temporary.Once they haven't looked for a job in the past four weeks are no longer counted as unemployed or in the labor force. The BLS adds them to a group it calls the marginally attached. For more, see Labor Force Participation Rate.
Among them are the discouraged workers, who have given up looking for work altogether. Others have gone back to school, gotten pregnant, or have become disabled. They may or may not eventually return to the labor force, depending on their circumstances. Once they haven't looked for a job in 12 months, they're no longer counted as marginally attached.
(Source: "Definitions," Bureau of Labor Statistics.)
The BLS includes part-time workers in the employment numbers. It asks whether they would prefer a full-time job. Those people are considered underemployed.
The U-6, or real unemployment rate, includes everyone who wants a full-time job but doesn't have one.
It counts the marginally attached (including discouraged workers) and the part-timers who would prefer a full-time job. As a result, the real or true unemployment rate is much higher.