USSR stands for Union of Soviet Socialist Republics, although it is also known as CCCP (the same acronym in Russian) or Soviet Union. It was a federal state based on Marxist socialism (the first in the world) that was established in 1922 and was definitively dissolved in 1991 due to the many economic and political problems that had plagued it since the 80s.
Its origin is in the Russian revolution (1917), which was the fall of the tsarist regime. This led to a Provisional Government that was soon eliminated and replaced by one of communist ideology. Soon the USSR or, as its residents called it, the Union (Soyuz in Russian) would be born.
Between 1940 and 1991, the USSR was divided into 15 republics: Armenia, Azerbaijan, Belarus, Estonia, Georgia, Kazakhstan, Kyrgyzstan, Latvia, Lithuania, Moldova, Russia, Tajikistan, Turkmenistan, Ukraine and Uzbekistan. Together they formed a federal union, although in reality they had little power. This fell almost entirely to the central government, located in the Russian Federal Soviet Republic (RSFSR).
The USSR was controlled by the Communist Party at all levels, its secretary general being the most powerful leader in the country. Soviet industry was owned by the state, who also managed it. For this purpose, he took the agricultural lands of the country and divided them into state farms, collective farms (known as sovjoses and kolkhozes, respectively) and small privately owned plots.
In addition to its highly centralized government and economy, another feature of the USSR was its political repression, despite which it emerged as one of the only two world superpowers after World War II. The other was the United States.