Visa: A U.S. visa allows the bearer to apply for entry to the U.S. in a certain classification (e.g. student (F), visitor (B), temporary worker (H)). A visa does not grant the bearer the right to enter the United States. The Department of State (DOS) is responsible for visa adjudication at U.S. Embassies and Consulates outside of the U.S. The Department of Homeland Security (DHS), Bureau of Customs and Border Protection (BCBP) immigration inspectors determine admission into, length of stay and conditions of stay in, the U.S. at a port of entry. The information on a nonimmigrant visa only relates to when an individual may apply for entry into the U.S. DHS immigration inspectors will record the terms of your admission on your Arrival/Departure Record (I-94 white or I-94W green) and in your passport.
Visa Waiver Program: Allows citizens of certain selected countries, traveling temporarily to the United States under the nonimmigrant admission classes of visitors for pleasure and visitors for business, to enter the United States without obtaining nonimmigrant visas. Admission is for no more than 90 days. The program was instituted by the Immigration Reform and Control Act of 1986 (entries began 7/1/88). Under the Guam Visa Waiver Program, certain visitors from designated countries may visit Guam only for up to 15 days without first having to obtain nonimmigrant visitor visas.
Voluntary Departure: The departure of an alien from the United States without an order of removal. The departure may or may not have been preceded by a hearing before an immigration judge. An alien allowed to voluntarily depart concedes removability but does not have a bar to seeking admission at a port-of-entry at any time. Failure to depart within the time granted results in a fine and a ten-year bar to several forms of relief from deportation.