What does the DC part in Washington D.C. mean?

Answer 1

The DC part in the name "Washington, D.C." means "District of Columbia.

When the capitol was first decided to be at that location the states of Virginia and Delaware each donated land sufficient to make a 10-mile square territory that would not be part of either state but would be controlled by the Congress. This district was called the District of Columbia. The city of Washington was originally only a small part of the district, but has grown to fill it all.

The part of the District on the Virginia site of the Potomac River was returned to Virginia many years ago, when the city was small and it was thought that the land would not be needed.
District of Colombia

Answer 2

DC Means District of Columbia!

So the full name is Washington, District of Columbia