Gesso is a white paint mixture that acts as a primer to prepare rigid surfaces for painting. It is made from a combination of chalk, pigment, and a binder, traditionally rabbit skin glue. The word "gesso" comes from the Italian word for "chalk". Using gesso helps create an even, slightly textured surface for paint to adhere to, preventing paint from soaking into the canvas. It also protects the canvas fibers and provides flexibility to prevent cracking.