A collage is a work of art formed by pasting together fragments (parts) of printed matter, cloth, or other light weight materials on surface. In French, the word collage means, "to glue". When creating a collage, an artist pastes, or glues, together materials, just like the terms means.
This is a stained glass piece, found in the Chartes Cathedral in France. We can see how light coming through behind creates a colorful and illuminating image.
