Categorical data is data with a predefined set of values. Using “Child,” “Adult,” or “Senior” instead of a person’s age as a number is one example of age categorization. However, before using categorical data, one must know about various forms of categorical data
First of all, categorical data may or may not be defined in an order. To say that the size of a box is small, medium, or large means that there is an order described as small < medium < large. The same does not hold for, say, sports equipment, which could also be categorial data, but differentiated by names like dumbbell, grippers, or gloves; that is, you can order the items on any basis. Those that can be ordered are known as “ordinal” while those where there is no such ordering are “nominal” in nature.