Form I-94, also called the Arrival/Departure Record of Stay Permit, is the small white card given to you at the port of entry to the U.S.  This form is very important since it officially determines how long an international student can remain in the U.S. Students on the F-1 and J-1 visas usually have their I-94 stamped "D/S" (Duration of Status) which means that the student can remain in this country for the length of time required to complete his/her studies as long as the student follows all of the regulations of the student visa.  The eleven digit number written on your I-94 is your INS admission number which is used by the INS to monitor your entry into and departure from the U.S.  This number will be your admission number for the duration of your program of study in the U.S.

If you are on a visa other than an F or J, or if you have a specific date stamped on your I-94 card instead of the "D/S" designation, you must apply for an extension or exit the US before the expiration date or you will be considered out of status and a visa overstay, which can have serious INS consequences.