Labor force participation rate uses the definition described by the OECD: the labor force divided by the total working-age population, where the 'working age' population refers to people aged 15 to 64.
Many people think that automation will reduce the number of jobs available. This would push people either into unemployment or perhaps out of participation in the workforce altogether. If some predictions are borne out, we could have substantially fewer people working. This has all sorts of implications. What sort of social support will people need if they cannot find a job? If work is redundant, is it necessary to have an economy that incentivizes work? Geopolitically, right now many countries (e.g., China, Japan) are worried about their aging workforces and low birthrates. Will automation make labor redundant in the end anyway?
"Unemployed" is a slightly different category which refers to people who want a job but do not have one. "Labor force participation" refers to the number of working people divided by the total number of working aged people.
See recent participation rates here: https://www.bls.gov/emp/tables/civilian-labor…
What will be the average US labor force participation rate for the decade 2040-2049?
This resolves to the US Bureau of Labor Statistics' Civilian Labor force participation rate, taking the average of all years from 2040 to 2049 inclusive, restricting age range to between 15 to 64 inclusive.
If the Bureau does not publicly provide precisely that age range - for instance, if it only provides statistics for 16 year or older - then the nearest publicly provided data applies.
Appropriate data that provides for yearly or better measurements or estimates of the labor force participation rate should be used.
If the US Bureau of Labor no longer exists or does not collect appropriate statistics, this contract resolves to other relevant sources, prioritizing sources within US government, then intergovernmental sources like the OECD, and then appropriate private US-based and international sources.