The I-94 card is an admission document which controls the status of nonimmigrant foreign nationals while they are present in the United States. The I-94 card is also used to track a person’s admission to and departure from the U.S.
The bottom portion of the I-94 reflects the traveler’s name, date of birth, country of citizenship, date of entry to the U.S., the class of admission (for example, B-1, F-1, H-1B, etc.), and the date on which the traveler’s status expires. It is a small white card which is stapled to the traveler’s passport when they clear Immigration at a port of entry to the U.S. I-94 cards are also attached to the USCIS approval notices for changes or extensions of status which are filed while the applicant is in the U.S.
When the traveler departs the U.S., they turn in the I-94 document to the airline representative. The airlines then forward the document to U.S. Customs and Border Protection (CBP), which then has a record of the person’s departure from the U.S. (hopefully) within their period of authorized stay.