Invert sugar (sold to bakers and confectioners as trimoline) is a thick, clear-to-pale-gold syrup or soft paste made by splitting ("inverting") table sugar into its two building-block sugars, glucose and fructose. That split is its whole point: the free-sugar mixture resists crystallising and pulls moisture from the air, so a spoonful keeps cakes, ganache, ice cream and fondant soft, smooth and moist far longer than plain sugar would.