USSR stands for Union of Soviet Socialist Republics, which was a communist state that existed from 1922 to 1991. It was a federal sovereign state in northern Eurasia, comprising a total of 15 republics. The USSR was known for its centralized government, planned economy, and influential role in global politics during the Cold War.
Note: The provided meaning of the answer is for the latest New York Times crossword puzzle clue: Old map letters. Explanations are generated by AI and may be inaccurate.