This is a process that is applied to denim fabric, usually after the singeing process, and adds starch to the fabric to stiffen the textile.
When the design patterns are cut from a pile of 40 layers of denim at a time, this makes sure the textile doesn’t move or fold. When raw denim is produced this starch creates the stiffness of the fabric. Some denim heads nowadays apply the starch by hand to foster the whiskering process.
Source: Nouvelle de Nîmes Nº 5: The Denim Dictionary