This paper studies the linguistic variability in Italian music songs from a social point of view, a new research approach with only few studies in the current bibliography. The social factors of linguistic variation will be called into question to discuss the meaning of "folk song", a rather complex notion. First of all, we shall remark that many recent studies on songs use the term 'popular' with a quite different meaning rather than the meaning used in Italian linguistics. The variationist approach allows us to define the meaning of "folk song", because it shows the close relationship between linguistic features and the social world represented in folk songs. In this perspective, we shall be taking into account the expressions of the 'folk' both in Italian songs and in the ones in dialect. On one hand, we shall be discussing the work conducted by researchers in ethnomusicology between the first and the second half of the 20th century showing how this work has led to the preservation of an important heritage for Italian culture. On the other hand, we will consider the relationships between this kind of work and the internal situation of the Italian linguistic repertoire.