The labour force is everyone of working age who has a job or is looking for one. The unemployment rate is the jobless share of it. People not looking for work, such as retirees and full-time students, are outside the labour force and not counted.
Australia's figure comes from the monthly ABS Labour Force survey; the US figure from the monthly household survey in the jobs report.
Why it matters
A tight labour market, with low unemployment, pushes wages up as employers compete for staff, which can feed inflation. A rising rate signals slack and usually comes before weaker spending. Central banks weigh it directly when setting rates.
See the data: Australian unemployment, US unemployment.
General information, not advice.