By not counting discouraged workers as unemployed it understates the unemployment rate. Official data include that all part-time workers as fully employed. However, some economist argue that people who work part time, but are willing to work full time should be considered as semi-hidden unemployed. Therefore, the BLS data understates the unemployment rate. Labor participation rate is the proportion of working age persons who are in the labor force.
Structural unemployment is due to changes in the structure of the economy or demand for labor.
The change may be also due to geographic distribution of jobs. Seasonal unemployment is the unemployment that fluctuates with the seasons of the year. Full employment is the level of frictional and structural unemployment. Full employment does not mean zero unemployment. The full employment of unemployment rate is also referred to as the natural rate of unemployment.