There was a rumor in the Soviet Union that The Beatles had secretly visited the U.S.S.R. and given a private concert for the children of top Communist party members. They believed the song "Back In The U.S.S.R." was written because of the concert. Actually, some fans still believe so.
ABBA's Bjorn Ulvaeus and Benny Andersson conceived "Dancing Queen" as a dance song with the working title "Boogaloo," drawing inspiration from the 1974 George McCrae disco hit "Rock Your Baby." Their manager Stig Anderson came up with the title "Dancing Queen."