Victory Day is a holiday that commemorates the victory of the Soviet Union over Nazi Germany in the Great Patriotic War. It was first inaugurated in the 16 republics of the Soviet Union, following the signing of the German Instrument of Surrender late in the evening on 8 May 1945. The Soviet government announced the victory early on 9 May after the signing ceremony in Berlin. Though the official inauguration occurred in 1945 the holiday became a non-labour day only in 1965 and only in certain Soviet republics.
In East Germany, 8 May was observed as "Liberation Day" from 1950 to 1966, and was celebrated again on the 40th anniversary in 1985. In 1975, a Soviet-style "Victory Day" was celebrated on 9 May.—Wikipedia