You will often hear visa classifications referred to in shorthand by a letter followed by a number. The following list explains the non-immigrant visa classifications available.

A-1 Ambassadors, public ministers, consular officers or career diplomats and their immediate families.
A-2 Other foreign government officials or employees and their immediate families.
A-3 Personal attendants, servants or employees and their immediate families, of A-2 visa holders.
B-1 Temporary business visitors.
B-2 Temporary tourist visitors.
C-1 Foreign travelers in immediate and continuous transit through the U.S.
D-1 Crewmembers (sea or air)
E-1 Treaty traders and their spouses or children
E-2 Treaty investors and their spouses or children
F-1 Academic or language students
F-2 Spouses or children of F-1 visa holders
G-1 Designated principal resident representatives of foreign governments coming to the U.S. to work for an international organization, their staff members and immediate families
G-2 Other representatives of foreign governments Coming to the U.S. to work for an international organization, and their immediate families
G-3 Representatives of Foreign Governments and their Immediate families who would ordinarily qualify For G-1 or G-2 visas except that their government Are not members of an international organization
G-4 Officers or employees of international organizations and their immediate families
G-5 attendants, servants and personal employees of G-1 through G-4 visa holders, and their immediate families
H-1B Aliens working in specialty occupations requiring at least a bachelor’s degree or its equivalent on the-job experience
H-2A Temporary agricultural workers coming to the U.S. to fill positions for which a temporary shortage of American workers has been recognized by the U.S. Department of Agriculture
H-2B Temporary workers of various kinds coming to the U.S. to perform temporary jobs for which there is a shortage of available qualified American workers
H-3 Temporary trainees
H-4 Spouses or children of H-1A/B,H-2A/B or H-3 Visa holders I Representatives of the foreign press coming to the U.S. to work solely in that capacity, and their immediate families
I Press Representatives
J-1 Exchange visitors coming to the U.S. to study, work or train as part of an exchange program officially recognized by the U.S. Information Agency
J-2 Spouses or children of J-1 visa holders
K-1 Fiance (e) of U.S. citizens coming to the U.S. for the purpose of getting married
K-2 Children of K-1 visa holders
K-3 Spouses of U.S. citizens awaiting approval of their immigrant visa petition or the availability of a green card
K-4 Children of K-3 visa holders
L-1 Intra-company transferees who work as managers, executives or persons with specialized knowledge
L-2 Spouses or children of L-1 visa holders
M-1 Vocational or other nonacademic students
M-2 Immediate families of M-1 visa holders
N Children of certain special immigrants
NATO-1 Principal permanent representatives of member states NATO ---including any subsidiary bodies, resents in the U.S. and resident official staff members, secretaries general, assistant secretaries general and executive secretaries of NATO, other permanent NATO officials of similar rank, or their immediate families
NATO-2 Other representatives to member states to NATO—including any subsidiary bodies, including its advisers and technical experts of delegations, members of Immediate article 3 , 4 UST 1796 Families; dependents of members of forces entering in accordance with the Status-of Forces Agreement or in a accordance with the Protocol on Status of International Military Headquarters; members of such a force issued
NATO-3 Official clerical staff accompanying representatives of member states to NATO – including any subsidiary bodies, or their immediate families
NATO-4 Officials of NATO – other than those who can be classified as NATO – 1, or their immediate families
NATO-5 Experts other than officials who can be classified NATO-1, employed on missions in behalf of NATO, and their dependents
NATO-6 Members of civilian components accompanying forces entering in accordance with provisions of the NATO Status-of-Forces Agreement; members of civilian components attached to or employed by allied headquarters under the Protocol on Status of International Military Heqadquarters set up pursuant to the North Atlantic Treaty, and their dependents
NATO-7 Attendents, servants or personal employees of NATO- through NATO-6 classes or their immediate families
O-1 Aliens of extradordinary ability in the sciences, arts, education, business or athletics
O-2 Support staff of O-1 visa holders
O-3 Spouses or children of O-1 nor O-2 visa holders
P-1 Internationally recognized athletes and entertainers
P-2 Artists or entertainers in reciprocal exchange programs
P-3 Artists and entertainers coming to the U.S. to give culturally unique performances in a group
P-4 Spouses or children of P-1, P-2 or P-3 visa holders
Q-1 Participants in international cultural exchange programs
Q-2 Immediate family members of Q-1 visa holders
R-1 Aliens in religious occupations
R-2 Spouses or children of R-1 visa holders
S-1 Certain aliens supplying critical information relating to a criminal organization or enterprise
S-5/6 Certain aliens supplying critical information relating to terrorism
S-7 Immediate family members of S-1 visa holders
T Women and children who are in the United States because they are victims of trafficking, who are cooperating with law enforcement and who fear extreme hardship (such as retribution) if returned home.
TN NAFTA professionals.
TD Spouses or children of NAFTA professionals.
V Spouses and children of lawful permanent residents who have been waiting for three years or more to qualify for a green card.