Gouache, also spelled guache, is a type of paint. It is also commonly called poster paint. It consists of pigment, a binding agent (usually gum arabic), and some additives to make it opaque. An inert, white pigment such as chalk is usually added. The essential idea is that gouache covers up whatever is underneath. Water colours, in contrast, are somewhat transparent.
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.