What does the D.C. stand for in Washington, D.C.?

Washington, D.C. is the capital of the United States. It is coterminous with the District of Columbia (abbreviated as "D.C.")

http://en.wikipedia.org/wiki/Washington,_D.C.

The District of Columbia was administered by three commissioners appointed by the president, until Nov. 3, 1967 when a mayor-commissioner and a 9-member council, appointed by the president, took office. On May 7, 1974, a Home Rule Charter was approved, giving DC its first elected municipal government in over a century. The district has one nonvoting member in the House of Representatives and an elected Board of Education.

http://www.infoplease.com/ipa/A0108620.html

D.C. stands for District of Columbia. It is called District of Columbia, because it was built on land of the Territory of Columbia, a 10 square mile piece of land, that used to be part of Virginia and Maryland. The territory of Columbia was named such after Christopher Columbus.