The Collaborative International Dictionary of English v.0.48:

Transparency \Trans*par"en*cy\, n.; pl. Transparencies. [Cf.
   F. transparence.]
   1. The quality or condition of being transparent;
      transparence.
      [1913 Webster]

   2. That which is transparent; especially, a picture painted
      on thin cloth or glass, or impressed on porcelain, or the
      like, to be viewed by natural or artificial light, which
      shines through it. --Fairholt.
      [1913 Webster]

WordNet (r) 3.0 (2006):

transparency
    n 1: permitting the free passage of electromagnetic radiation
         [syn: transparency, transparence] [ant: opacity]
    2: the quality of being clear and transparent [syn:
       transparency, transparence, transparentness]
    3: picture consisting of a positive photograph or drawing on a
       transparent base; viewed with a projector [syn: foil,
       transparency]