Technique of painting with pigments dispersed in molten wax. It is applied while warm to panels or murals with a brush or palette, and fixed by passing a heat source over the surface to fuse and permanently bond the paint. It is an ancient technique that was particularly popular in ancient Greece. The term derives from a Greek word meaning 'burnt in.' Although it fell into disuse in the 8th or 9th centuries C.E., there continue to be exponents of the technique today. For the technique of decorating clay, use "encaustic decoration."
Source: Art & Architecture Thesaurus

http://vocab.getty.edu/page/aat/300053353