The government calls this number:
Marginally attached workers are persons who currently are neither working nor looking for work but indicate that they want and
are available for a job and have looked for work sometime in the recent past. Discouraged workers, a subset of the marginally attached,have given a job-market related reason for not looking currently for a job. Persons employed part time for economic reasons are those who want and are available for full-time work but have had to settle for a part-time schedule. For more information, see "BLS introduces new range of alternative unemployment measures," in the October 1995 issue of the Monthly Labor Review. Updated population controls are introduced annually with the release of January data.
This is a truer, but not entirely true(due to the modeling methodologies used by the government since the Nixon Administration) of un- and under-employment in the United States. Currently, that number is 10.3 percent, far larger than the U3 number, a measurement of new unemployment enrollees.
Bureau of Labor Statistics U6 Report
More on America's Real Unemployment Rate