Today's Employment Situation report showed that in March, total unemployment -- including all marginally attached workers -- declined notably to 13.8%, while the traditionally reported unemployment rate also trended down to 7.6%. The traditional unemployment rate is calculated from the monthly household survey results using a fairly explicit definition of "unemployed" (essentially, it's the unemployed and those currently looking for full-time employment), leaving many workers to be considered effectively "on the margin." That means they're either employed in part-time work when full-time is preferred, or simply unemployed and no longer looking for work.
The Bureau of Labor Statistics considers marginally attached workers (including discouraged workers) and persons who have settled for part-time employment to be "underutilized" labor. The broadest view of unemployment would include both traditionally unemployed workers and all other underutilized workers. To calculate the total rate of unemployment, we would simply use this larger group rather than the smaller and more restrictive unemployed group used in the traditional unemployment rate calculation.