Source: http://uslex.com/Non-Immigrant-Visas/Diplomatic-Visas/A-G-C-Visas.html
Timestamp: 2019-04-22 20:26:28+00:00

Document:
A Visas are issued pursuant to INA §101(a)(15)(A), 8 U.S.C. §1101(a)(15)(A). A visas are issued to diplomats, officials and employees of foreign governments recognized by the U.S. coming on official business.
A-l Visas are issued pursuant to INA 22 C.F.R. §41.22(b). Ambassadors, public ministers or career diplomats/officers and their immediate families.
A-2 Visas are issued to other accredited officials and employees of foreign governments and their immediate families.
A-3 Visas are issued to attendants, servants, personal employees of A-1 or A-2 and members of their immediate families.
G Visas are issued pursuant to INA §101(a)(15)(G), 8 U.S.C. §1101(a)(15)(G), 9 FAM 41.24. G visas are issued to a designated principal resident representative of a foreign government recognized de jure by the United States, which foreign government is a member of an international organization entitled to enjoy privileges, exemptions, and immunities as an international organization under the International Organizations Immunities Act (59 Stat. 669) 22 U.S.C. 288, note, accredited resident members of the staff of such representatives, and members of his or their immediate family.
C-2 visas also called UN transit visas are issued to representative(s) (from non-de jure and nonmember country, e.g., Hamas official Abu Marzouk), or to expert(s) that U.N. needs.
C-2 visa holders are given 29 days. Must stay within NYC area and proceed directly to U.N. When leaving U.N. business must leave U.S. 8 C.F.R. §214.2(c)(2).
C-3 Visas are issued to accredited official(s) of foreign government passing in transit through U.S. on official business and U.S. has reciprocal right in foreign country.

References: §101
 §1101
 §41
 §101
 §1101
 §214