Overstay means staying in the U.S. beyond the date indicated on your I-94 or the stamp in your passport or the corresponding Duration of Status (D/S) – even for one day. Overstay is one of the acts that causes you to be “out of status.” It is a violation of U.S. immigration laws and it results in your visa being automatically voided. In this situation, you are required to reapply for a new non-immigrant visa but it may even cause you to be ineligible for a visa in the future for return travel to the U.S. – depending on how long you were out of status.
Individuals who have the endorsement of D/S, but who are no longer performing the same function in the U.S. that they were originally admitted to perform (i.e. no longer working for the same employer or no longer attending the same school) can only overstay if the DHS or an immigration judge makes a specific finding of status violation.
A visa is a document or actually a sticker inside your passport that allows you to enter the US from a foreign country, much like a ticket to a movie theater. You must apply and obtain that visa (ticket) at the US consulate/embassy (box office) in your home country before coming to the US (entering the theater).
A visa is only used to enter the US, but doesn’t say anything about how long you can stay. To stay in the US, you must have legal status.
After you have entered the US using your visa, you must maintain legal status. Legal status allows you to legally stay in the US until the expiration date stamped in your passport or on your I-94 form, the white piece of paper commonly stapled in your passport. Earlier this year, CBP (Customs and Border Patrol) digitized the I-94 process and one does not get a paper anymore. However, the date in the passport still dictates how long you can stay. When this date is up, so is your legal status.
Please note, your visa may have a way longer expiration date than the stamp in the passport. This only means that you can leave and enter the US with the same visa up until the visa expiration date.
Unlawful presence is the presence in the U.S. after the expiration of the period of stay authorized by an Immigration Inspector/Customs Officer, or any presence without being inspected by an Officer and admitted or paroled. The authorized period of stay is normally either noted on the I-94 or the stamp in your passport.
Persons who remain in the U.S. beyond their authorized stay are not able to extend their stay in the US or change their status to another non-immigrant status. In most cases they are also barred from adjusting their status from that of a non-immigrant to that of an immigrant.
Persons who remain in the U.S. beyond their authorized stay for more than 180 days, and then leave the US, are barred from reentering the U.S. for three years from their date of departure.
Persons who remain in the U.S. beyond their authorized stay for more than one year, are barred from reentering the US for ten years from their date of departure.
Persons who commit fraud or material misrepresentation are barred from the U.S. permanently.