ABOUT ESTA
ESTA is short for the "Electronic System for Travel Authorization." ESTA is an application system for all travelers from Visa Waiver Countries. The Visa Waiver Program has made visiting the United States very easy for millions of visitors with a machine readable passport. Now, due to heightened security regulations, the same visitors must apply for a Travel Authorization in advance. As always, a passport from a Visa Waiver country is still required to gain admittance to the country. The entire application process is conducted online and operated by the U.S. Department of Homeland Security (DHS).
The Travel Authorization is not a visa. In fact, a person from a non-visa waiver country should not even attempt to apply for a Travel Authorization. The purpose of ESTA is to allow DHS to pre-screen all Visa Waiver Travelers before they leave their respective countries. US bound travelers are recommended to apply for the Travel Authorization at least 72 hours prior to departure. An approved Travel Authorization is not a guaranteed entry, but a prerequisite to travel to the United States by air or sea carrier.
Visit http://www.esta.us/esta.html for more information and application