The Collaborative International Dictionary of English v.0.48:

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.
      [1913 Webster]

   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.
      [1913 Webster]

WordNet (r) 3.0 (2006):

camera obscura
    n 1: a darkened enclosure in which images of outside objects are
         projected through a small aperture or lens onto a facing
         surface