The Electronic System for Travel Authorization (ESTA) is an automated system used by the United States to determine the eligibility of visitors traveling to the country under the Visa Waiver Program. It allows travelers from participating countries to apply for authorization online before their trip, streamlining the entry process and enhancing security. Once approved, ESTA grants travelers permission to board a carrier bound for the U.S. and stay for up to 90 days for tourism or business purposes. This system helps the U.S. government assess potential risks and ensures a smoother travel experience for eligible visitors.