An I-94 is an arrival and departure record that is issued by a Customs and Border Protection officer, in either paper or electronic format, to foreign visitors entering the U.S.
Most arrival or departure records are now created electronically upon arrival. Visitors are provided with an annotated stamp in their foreign passport.
If provided a paper form, the admitting CBP officer generally attaches the I-94 to the visitor's passport and stamps the departure date on the form.
Visitors must exit the U.S. on or before that date stamped on the form or in the passport.