Three years of federal probation means a person avoids prison time for a federal crime but must live under strict court-ordered rules for three years, reporting to a probation officer, staying employed, avoiding drugs/crime, potentially wearing an ankle monitor, and facing immediate re-incarceration if they violate any conditions, says Wikipedia and Nolo. It's a sentence in place of jail, allowing community supervision with strict behavioral expectations set by the judge, notes Law Offices of Hope Lefeber and Gallian Firm.