how do I interpret this number?
From the wikipedia entry on focal length:


  Due to the popularity of the 35 mm standard, camera–lens combinations
  are often described in terms of their 35 mm equivalent focal length,
  that is, the focal length of a lens that would have the same angle of
  view, or field of view, if used on a full-frame 35 mm camera. Use of a
  35 mm-equivalent focal length is particularly common with digital
  cameras, which often use sensors smaller than 35 mm film, and so
  require correspondingly shorter focal lengths to achieve a given angle
  of view, by a factor known as the crop factor.