The B-2 visa is intended for individuals who will make short trips to the United States for pleasure. This category includes tourists, attendance at special events, visiting friends or family, medical treatment, etc.
A detailed list of qualifying B-2 visitor purposes is stated in the notes to http://www.state.gov/m/a/ips/c22793.htm
The applicant cannot intend to:
The Immigration and Naturalization Service may deny an application to change from B-2 status to another visa that allows work or study in the United States if they suspect that the B-2 visa was obtained with the intent to work or study in the United States.
B-2 states may be granted for a period of up to six months and extended for a total stay of one year. However, the period will be consistent with the applicant's purpose in the United States.