This is the Training/Student Visa.
It is very versatile and allows you to come to the United States to either get training or study at numerous institutions and organizations.
This visa allows you to get trained in areas of discipline ranging from the medical to the agricultural to business fields. 
This visa does not need prior Immigration and Naturalization approval, and therefore, can be obtained quickly.
You must have either a sponsoring school, organization or business.
It is sometimes easier to get this visa than the F-1 Student Visa, but does carry some other significant restrictions.