Opacity or opaque refers to something difficult to see through or perceive. It can refer to: Opacity (coal combustion), the ratio of coal to air in coal combustion literature. Opacity (optics), the degree to which light's blocked. Opaque context, a linguistic context in which it isn't possible to substitute co-referential terms while guaranteeing the preservation of truth values. Opaque travel inventory, the market of selling unsold travel inventory at a discounted price. In computer scienc… (More on Opacity)