- Without being admitted or paroled, or
- After the expiration of a period of stay authorized by the Department of Homeland Security (i.e., the visa has expired).
Unlawful presence is relevant only for determining admissibility. The problem begins if you accrued unlawful presence of over 180 days or 365 days. You will be barred from returning for 3 years (if over 180 but less than 365) or 10 years (if over 365 days). These unlawful presence bars are commonly known as the 3- and 10-Year Bars.
If you are, for example, approved for Deferred Action, you can not be accruing unlawful presence but that doesn’t mean you have lawful status in the US. Moreover, if you accrued unlawful presence before achieving lawful status, you may still have a problem when you seek to return to the U.S.