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 visa (WT).
https://cbocalbos.wordpress.com/tag/212d3-waiver/
https://cbocalbos.wordpress.com/tag/212c-waiver-application/