what does "NW" stand for?
【He even revised White House protocol in his behalf. Convention, for example, required that when the two men attended ceremonial occasions together the President should slowly descend the executive mansion's Grand Staircase alone while his Vice President sneaked down in an elevator. Kennedy ordered that Johnson accompany him, be photographed with him, greet guests with him. The Vice President, in other words, was to act as though he lived in the house. But the blunt truth was that he didn’t live there. Nothing could alter the fact that his real address was 4040 Fifty-second Street, NW. The chasm remained intractable.】
I need to figure out the Johnson's address mentioned here. what does "NW" stand for? thx~