Waiver for Unlawful Presence
Unlawful presence usually occurs for two reasons: (1) The person entered the United States illegally, therefor the do not have a legal presence in the United States (2) A person has stayed past the date they were required to leave on their visa. In the first scenario, the person would be barred from reentering the United States for 3 years. However, in the second situation the person has 180 past their date they were supposed to leave before they become barred.
The most common reason this occurs is because someone is already past their time and are barred, they therefor see no reason to leave since it will take so long to gain access to another visa. This is dangerous thinking, because if they are caught they can be immediately deported. However, it is not entirely over at that point. This person may apply for a waiver of unlawful presence.
The waiver of unlawful presence can have this barred period “waived” or forgiven. If approved the person must return to their country of origin and reapply for an immigration visa.