A **vector of categorical variables** is a one-dimensional matrix or set of values where each value is an assignment to a finite number of variables (cf. vector of quantitative variables). For example, if a house is white and terraced, these two facts make up a vector of categorical variables that describe it.

In this catalogue, we subsume under categorical variables probabilities that a value belongs to a given class. These are expressed as a number between 0 and 1 and are thus fundamentally different from quantitative variables with their potentially infinite ranges.