WT/WB Visa Waiver
There are many countries in the world that do not require formal issuance of a visa to visit the United States. If you are from one of those countries, then you are eligible to come in on either the visa waiver for pleasure as a tourist (WT), or the visa waiver for business (WB). You can stay only 90 days once you enter the United States.
Once you get to the United States, you cannot change or adjust your status to any other type of visa. Therefore, you may want to consider other types of visa in order to remain in the United States for longer periods of time.