1, The full form of USSR is Union of Soviet Socialist Republics. It’s used on Regional ,Countries in Worldwide

Union of Soviet Socialist Republics (USSR), also known as the Soviet Union, was a socialist state that existed from 1922 to 1991, consisting of Russia and many surrounding countries in Asia and Europe. USSR was a union of 15 Socialist republics: Russia, Georgia, Ukraine, Moldova, Belarus, Armenia, Azerbaijan, Kazakhstan, Uzbekistan, Turkmenistan, Kyrgyzstan, Tajikistan, Latvia, Lithuania, Estonia.

2, The full form of USSR is Uninterrupted Sustained Silent Reading. It’s used on Academic & Science ,Daycare & Preschool in Worldwide

Uninterrupted Sustained Silent Reading (USSR) or Sustained Silent Reading (SSR), is defined as a period of uninterrupted silent reading for a specific amount of time (typically 10 to 30 minutes). It is a school-based recreational reading, where students choose something to read that is of high interest to them.