Candy is often used as a synonym for the more general term confectionery in North America, whereas the word has become archaic in most parts of the United Kingdom and survives today almost exclusively in the term "candy floss". In some areas, notably Scotland, "candy" is generally taken to mean confectionery made from crystallized sugar. In the United Kingdom in general, a piece of confectionery is referred to as a sweet. In Australian English, all such confections are collectively referred to as lollies. In New Zealand English, both terms are used.

Candies are prepared by dissolving sugar in water or milk to form a syrup, and boiling it until it starts to caramelize. Depending on the solvent and the end result of the process, the product may be called candy, caramel, toffee, fudge, praline, tablet or taffy. The recipe used also predicts how hard, soft, chewy or brittle the end result should be.

The eventual texture of candy depends on the temperature to which the sugar solution is boiled, since the presence of a solute in a liquid elevates the boiling point of the liquid. Increasing the sugar content will also raise the boiling point. As the syrup is heated, it boils, which causes the sugar concentration in the syrup to increase due to evaporation of the water, which raises the boiling point even further. The relationship between the boiling point and the sugar concentration is predictable, and so heating the syrup to a particular temperature ensures a particular sugar concentration with some accuracy. In general, higher temperatures — which imply greater sugar concentrations — result in hard, brittle candies, and lower temperatures result in softer candies. These "stages" of cooking candy have been named and correlated with the cooking temperatures, and is frequently specified in recipes:

* "thread": 230-233°F / 110-111°C

* "soft-ball": 234-240°F / 112-115°C

* "firm-ball": 244-248°F / 118-120°C

* "hard-ball": 250-266°F / 121-130°C

* "soft-crack": 270-290°F / 132-143°C

* "hard-crack": 295-310°F / 146-154°C

This unusual nomenclature derives from the process used to test the syrup in times before thermometers became affordable. A small spoonful of the hot syrup was dropped into a glass of cold water. The characteristics of the resulting lump of sugar could then be used to determine the concentration of the syrup. "Thread" stage produces long strings of hardened sugar, while "ball" stages result in a smooth lump with the corresponding hardness described. The "crack" stages create a ball of candy so brittle that the rapid cooling from the water literally causes it to crack. This method is still used today in some kitchens; however, a candy thermometer is much more accurate.

Once the syrup reaches 340°F or higher, the sucrose molecules break down into many simpler sugars, creating an amber-colored substance known as caramel. This should not be confused with caramel candy, although it is the candy's main flavoring agent.