Mass song Russian: массовая песня was a genre of the Soviet music, widespread in the Soviet Union. A mass song was a song typically written by a professional or amateur composer for individual or chorus singing and intended for "broad masses" of Soviet people. 
The Soviet mass song is a representative of the school of Socialist realism in art and important part of the Soviet propaganda;  as the Soviet Music Eclyclopedia puts it, they were "a powerful means of organization and education of the masses".
According to the Soviet Music Encyclopedia, during 1920-1950s the term was applied to most of the songs written by the Soviet composers. However with the establishment of the term "Soviet song," the term "mass song" was restiriced to the genre of chorus songs without accompaniment and with lyrics based on social-political themes, typically performed during various Soviet gatherings: rallies, demonstrations, meetings, etc. Some songs of other Soviet song genres, "stage song" (estradnaya pesnya) and "everyday song" ("bytovaya pesnya"), could also considered to be "mass songs", depending on their social importance. 
Musical characteristics of a mass song ensured easy comprehension and performance by non-professional "masses". A mass song is typically an alternaning sequence of four-line stanzas and refrains in a nonsophisticated musical form which employed most common vocal register. Typically these songs are of optimistic or heroic character, written in the form of a march.
A significant number of mass songs were film soundtracks.
- "Mass Song", Music Encyclopedia (Музыкальная энциклопедия. — М.: Советская энциклопедия, Советский композитор. Под ред. Ю. В. Келдыша. 1973—1982.) (Russian)
- Schwarz, Boris. Music and Musical Life in Soviet Russia. 1972. New York: W. W. Norton, 1972.
- Olkhovsky, Andrey. Music under the Soviets. 1955. Westport: Greenwood Press, 1975.