A matte, opaque watercolor paint typically having gum arabic, gum senegal, or dextrin as a binder. Gouache paints differ from watercolor paints, which use transparent pigments. Chalk and other white fillers may be added to some colors. Gouache was used for miniature paintings in the 16th-18th centuries, for decorative paintings on interior walls, and for printing wall paper patterns. Poster paints are an inexpensive version of gouache. The term originally had a different meaning, referring to oil applied on top of tempera painting.
Source: Art & Architecture Thesaurus
http://vocab.getty.edu/page/aat/300070114
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