Mosaic is the art of creating images with an assemblage of small pieces of colored glass, stone, or other material. It may be a technique of decorative art, an aspect of interior decoration or of cultural and spiritual significance as in a cathedral. Small pieces, normally roughly cubic, of stone or glass of different colors, known as tesserae, are used to create a pattern or picture.
(reference: http://en.wikipedia.org/wiki/Mosaic)