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