From the Document: "The official unemployment rate released on a monthly basis by the Bureau of Labor Statistics (BLS), also known as U3, measures the number of unemployed individuals as a percentage of the entire labor force. It is important to define these terms, as the BLS definitions are not entirely intuitive. The labor force is defined as all individuals aged 16 and over who are either unemployed or employed, excluding active duty military personnel. Individuals are considered employed if they did any work for pay or profit in the previous week. Individuals are considered unemployed if they satisfy the following three criteria: (1) they do not have a job, (2) they have actively looked for work in the previous four weeks, and (3) and they are currently available to work. If an individual does not have a job, but has not looked for work in the previous four weeks, and/or is not currently available for work that individual is not considered part of the labor force."
CRS In Focus, IF10443
Congressional Research Service: https://crsreports.congress.gov/