USA Visitor Visa:
Generally, a citizen of a foreign country who wishes to enter the United States must first obtain a visa, either a nonimmigrant visa for temporary stay, or an immigrant visa for permanent residence. The "visitor" visa is a nonimmigrant visa for persons desiring to enter the United States temporarily for business (B-1) or for pleasure or medical treatment (B-2), or combination of both (B-1/B-2) purposes.
Business Visitor Visas (B-1): As examples, if the purpose for your planned travel is to consult with business associates, travel for a educational, scientific, professional or business convention, or conference on specific dates, settle an estate, or negotiate a contract, then you would apply for a visitors visa.
Pleasure, Tourism, Medical Treatment - Visitor Visas (B-2): As examples, if the purpose of your planned travel is recreational in nature, including tourism, amusement, visits with friends or relatives, rest, medical treatment, and activities of a fraternal, social, or service nature, then you would apply for a vistors visa. The visa allows a foreign citizen, to travel to the United States port-of entry and request permission of the U.S. immigration inspector to enter the U.S.
     Persons planning to travel to the U.S. for a different purpose such as students, temporary workers, crewmen, journalists, etc., must apply for a different visa in the appropriate category.
     Representatives of the foreign press, radio, film, journalists or other information media, engaging in that vocation while in the U.S., require a nonimmigrant Media (I) visa and cannot travel to the U.S. using a visitor visa and cannot travel on the visa waiver program, seeking admission by the DHS immigration inspector, at the U.S. at the port of entry.
 Referer: http://travel.state.gov/visa/temp/types/types_1276.html
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