Source : Webster's Revised Unabridged Dictionary (1913)

Camera obscura \Cam"e*ra ob*scu"ra\ [LL. camera chamber + L.
   obscurus, obscura, dark.] (Opt.)
   1. An apparatus in which the images of external objects,
      formed by a convex lens or a concave mirror, are thrown on
      a paper or other white surface placed in the focus of the
      lens or mirror within a darkened chamber, or box, so that
      the outlines may be traced.

   2. (Photog.) An apparatus in which the image of an external
      object or objects is, by means of lenses, thrown upon a
      sensitized plate or surface placed at the back of an
      extensible darkened box or chamber variously modified; --
      commonly called simply {the camera}.

Source : WordNet®

camera obscura
     n : a darkened enclosure in which images of outside objects are
         projected through a small aperture or lens onto a facing
         surface