Viscous describes a fluid that is thick and moves slowly — honey, treacle, and heavy cream are viscous; water and wine are not. Viscosity is the measurable resistance to flow, and in food it is a defining texture attribute: the slow pour of a sauce, the cling of a glaze, the body of a soup all depend on it. Cooks control viscosity constantly — reducing to thicken, adding starch or gum, serving hot (heat thins most liquids) or cold. In processing, viscosity dictates pump and pipe design, mixing energy, and filling speeds. The human palate reads viscosity as richness, which is why low-fat products work so hard to mimic the viscosity of the full-fat originals.