What are the three- and ten-year bars?
The three- and ten-year bars are immigration policies that prohibit entry to the United States through a legal channel for some years. The bars are applied as an additional penalty for time spent in the U.S. without authorization, known as "unlawful presence". Individuals who accrue a certain amount of time of unlawful presence are inadmissible, or ineligible to receive a visa or adjust their status.
Remaining in the U.S. without authorization for more than 180 days but less than a year triggers a three-year bar; more than one year is a ten-year bar. An individual who stays without authorization long enough to trigger a bar and then reenters or attempts to reenter the U.S. without authorization is subject to a permanent bar. Individuals who remain in the U.S. without authorization are also subject to removal.
The unlawful presence bars are generally applied when an individual has remained in the U.S. without authorization, then leaves the country and attempts to reenter through a legal channel. If they had accrued enough unlawful presence to trigger a bar, they would be denied reentry until the time on that bar runs out.