The civilian labor force is the sum of employed and unemployed persons.
The series comes from the 'Current Population Survey (Household Survey)'.
Source: US. Bureau of Labor Statistics
Release: Employment Situation
US. Bureau of Labor Statistics, Civilian Labor Force - 4 years of High School, No Diploma, 25 years and over [HS4NL25O], retrieved from FRED, Federal Reserve Bank of St. Louis https://research.stlouisfed.org/fred2/series/HS4NL25O/, June 3, 2015.