ESTA is not a visa, although it is often referred to as one. ESTA stands for Electronic System for Travel Authorization under the Visa Waiver Program (VWP). There are 38 countries taking part of the VWP. Citizens of those countries may apply for an ESTA.
A successful ESTA application means its holders are granted a two-year authorization to travel to the United States. Each visit should not be longer than 90 days.
ESTA holders do not need to make a new application before each trip, as the travel authorization grants them the right to an unlimited number of trips. However, they must not overstay the 90-day period as this will have negative consequences on future ESTA or visa applications, as well as admission in the country.
A visa is a legal permit to enter the United States, which is required of all foreign citizens by law. Aliens who do not have a visa or any other legal authorization will not be allowed through the border control in the United States.
The two most common visa types are:
Both of those visas might be granted for a period of 1 to 6 consecutive months. However, unlike ESTA, those visas do not authorize for multiple entries. Furthermore, the visa application process required more documentation as proof of the traveller’s intention to return to his country of origin, after his trip the U.S. In addition, applicants must go through a one-to-one interview at a local U.S. embassy or consulate, which will be the final step of their application.
Making an ESTA application is significantly easier process. Citizens of any of the Visa Waiver countries should apply for an ESTA. Those who cannot participate in the Visa Waiver Program can apply for a B1 or a B2 visa.