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 - College Graduates - Master's Degree, 35 to 44 years, Men [CGMDLM3544], retrieved from FRED, Federal Reserve Bank of St. Louis https://research.stlouisfed.org/fred2/series/CGMDLM3544/, June 30, 2015.