Here's a short snippet from Wikipedia that illustrates it[1]:

   Bubblegum pop is a genre of pop music with
   an upbeat sound contrived and marketed to
   appeal to pre-teens and teenagers, that may
   be produced in an assembly-line process,
   driven by producers and often using unknown
   singers. Bubblegum's classic period ran from
   1967 to 1972. A second wave of bubblegum
   started two years later and ran until 1977

[1] https://en.wikipedia.org/wiki/Bubblegum_pop