Gouache

Gouache, also spelled guache, is a type of paint. It is also commonly called poster paint. It comprises pigment, a binding agent (usually gum arabic), and some additives to make it opaque. An inert white pigment such as chalk is usually added. Gouache covers up whatever is underneath. Water colours, in contrast, are somewhat transparent.
After gouache has dried, any form of paint can be used on the surface, also pastels and crayons. Watercolours on top of a gouache surface are not so runny (fluid) as they are on plain paper. 
The fast-drying quality of gouache makes it a favourite for "en plein air" (outdoor) paintings. It was also a favourite of J. M. W. Turner. 
Gouache also refers to paintings that use this type of paint.