Permission from a U.S. Consul to seek admission to the United States. A visa is issued subsequent to establishing eligibility for admission on a permanent basis under the Immigration and Nationality Act. Immigrant visas generally permit an alien to be admitted to the United States for permanent residency. It is necessary for the immigrant to apply for admission during this period, and they are generally valid for six months.
Is a document that signifies that a consular officer believes that the alien to whom the visa was issued is eligible to apply for admission in a particular nonimmigrant category. Visas may be valid for anywhere from 30 days to to 10 years. Visas can be limited to only a single entry or can be valid for multiple entries while they’re valid. These should be distinguished from the authorized period of stay which is give on the I-94, Arrival Departure Record.
The period of validity of a visa is not the same as authorized period of temporary stay in the United States. The authorized period of temporary stay, which is indicated on a small white card -- form I-94, Arrival Departure Record -- stapled into the passport, may be less than the period of validity of the visa, or may be much longer during the period during which the visa itself is valid. It is important to understand that it is always the I-94 and not the visa in the passport that determines a nonimmigrant alien’s status and its validity as to time and purpose. An alien is not out of status if he or she was properly admitted pursuant to a valid visa and the visa has expired, provided the person is still within the authorized period of stay indicated on form I-94.
However, a visa does not guarantee admission; an immigration inspector can deny entry if he or she believes that a particular alien is not eligible to be admitted in the category for which the visa was issued. The period of validity of a particular visa establishes the time during which the alien may present him or herself at a U.S. port of entry.