The Collaborative International Dictionary of English v.0.48:

collage \collage\ n.
   1. any picture made by sticking together pieces of paper or
      photographs, especially in unusual or surprising ways.

   Syn: montage.
        [WordNet 1.5]

   2. the technique of producing a work of art that is a
      collage[1].
      [PJC]

   3. any composite object, whether abstract or concrete,
      created by assembling components of varied types.
      [PJC]

   4. (Cinema) a film having scenes of different types or from
      different locations displayed in rapid succession without
      transitions.
      [PJC]

WordNet (r) 3.0 (2006):

collage
    n 1: a paste-up made by sticking together pieces of paper or
         photographs to form an artistic image; "he used his
         computer to make a collage of pictures superimposed on a
         map" [syn: collage, montage]
    2: any collection of diverse things; "a collage of memories"