What is an I-94 Card?
An I-94 card is a small green or white card given to all nonimmigrants entering the U.S. It serves as evidence that you have entered the country legally. On this card, an immigration inspector stamps either a specific date or “D/S” (duration of status). This card, rather than the visa in your passport, governs the authorized period of stay in the U.S. for any given visit.
If you are admitted to the U.S. until a specific date, and you overstay the I-94 card end date without filing a timely application for extension of stay or change of status, you will automatically void or cancel all the visas you may have in your passport. In addition, you may be required to obtain future U.S. visas only in your home country.