Fuzzy Variables are much like set variables in Pascal. However, unlike Pascal variables, the enumerated items, or terms, in the set are fuzzy and not crisp. Pascal allows enumerated values to either be in or not in the set. Fuzzy variables allow values to be partially in the set. For example, we may define a fuzzy variable which is based on Temperature. Any variable of this type may take fuzzy set (TFuzzySet) values of cold, warm, and hot (or some combination). Cold, warm, and hot are the fuzzy sets which define the terms of the type. Each fuzzy set defines a membership function over the domain of temperature. If, for our example, temperature has a range between 0 and 100 Celsius, Cold could be a fuzzy set that defined any value under 10 Celcius as completely cold (one or True), any value over 50 as not at all cold (zero), and any value in between having a membership between zero and one.
The most important function of the Fuzzy Variable is that it acts as the domain for its fuzzy sets. It defines the universe of discourse (the X range) over which values and sets in the variable may take. Before working with fuzzy sets, you must define a fuzzy variable. Fuzzy sets must have unique names.