What common cocktail ingredient is made from sugar and water?

Simple syrup is the correct answer because it is a solution made by dissolving equal parts of sugar and water, creating a sweet liquid that is commonly used in cocktails. Its balanced sweetness and easy incorporation into drinks make it a favorite among bartenders for sweetening beverages without the granularity of undissolved sugar.

Bitters, while they can be sweet, are typically a concentrated mixture infused with herbs, spices, and other flavorings, and do not fit the sugar and water definition. Sour mix is a mixture combining lemon or lime juice with sugar and water, but it includes additional acidity and flavor components, making it distinct from the simple syrup. Lime juice, on its own, is the juice extracted from limes and contains acids and flavors, rather than being a sugar-water mixture. Thus, simple syrup stands out as the quintessential sugar and water cocktail ingredient.