The Collaborative International Dictionary of English v.0.48:

Folk \Folk\ (f[=o]k), Folks \Folks\ (f[=o]ks), n. collect. & pl.
   [AS. folc; akin to D. volk, OS. & OHG. folk, G. volk, Icel.
   f[=o]lk, Sw. & Dan. folk, Lith. pulkas crowd, and perh. to E.
   follow.]
   1. (Eng. Hist.) In Anglo-Saxon times, the people of a group
      of townships or villages; a community; a tribe. [Obs.]
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            The organization of each folk, as such, sprang
            mainly from war.                      --J. R. Green.
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   2. People in general, or a separate class of people; --
      generally used in the plural form, and often with a
      qualifying adjective; as, the old folks; poor folks.
      [Colloq.]
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            In winter's tedious nights, sit by the fire
            With good old folks, and let them tell thee tales.
                                                  --Shak.
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   3. The persons of one's own family; as, our folks are all
      well. [Colloq. New Eng.] --Bartlett.
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   Folk song, one of a class of songs long popular with the
      common people.

   Folk speech, the speech of the common people, as
      distinguished from that of the educated class.
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WordNet (r) 3.0 (2006):

folk song
    n 1: a song that is traditionally sung by the common people of a
         region and forms part of their culture [syn: folk song,
         folksong, folk ballad]