Gesso is the Italian word for the white mineral gypsum. It is used as a ground or preparatory layer to ensure a smooth surface for painting or gilding on wood. It was also used for the preparation of a panel for gilding or the priming of canvas.
Also known as "glue gesso," a traditional mix of an animal glue binder (usually rabbit-skin glue) gesso prepares or "primes the surface for painting by making it slightly textured and ready to receive acrylic paint. Without gesso, the paint would soak into the weave of the canvas.