Coarse sugar, sometimes called turbinado or raw sugar, is minimally processed sugar that keeps some of the molasses from the sugar cane, giving it large, irregular, light-brown crystals instead of the fine white crystals of refined sugar. It's made by boiling and spinning cane juice to remove much of the molasses, but without the further refining and bleaching that produces white sugar.
The big crystals don't dissolve as readily as fine sugar, so coarse sugar is prized mainly for texture and appearance: sprinkled on cookies, muffins, and pastries for a crunchy, sparkling top, or used as part of a dry rub on meat, where it can caramelize into a flavorful crust. Its subtle molasses flavor also works well folded into marinades, glazes, and sauces that need a touch of sweetness and depth.
Coarse sugar shows up widely in baking across many cuisines, and in the US it's often marketed as a "more natural" alternative to refined white sugar, though nutritionally the difference between the two is minor.