Gesso is a glue-like paint, most often white, used a base or undercoat when preparing a canvas for painting.
Some types of gesso are extremely odoriferous. The gesso seals the pores in the canvas and provides a relatively smooth uniformly coloured surface for the artist to work on. Pre-gessoed canvases can be obtained commercially.
Gesso is also used by sculptors, to prepare the shape of the final sculpture (fused bronze) or directly as a material for sculpting.
"Gesso" is the Italian word for "chalk" (akin to the English word "gypsum"). A collection of gesso sculptures is properly called a gypsoteque.