The definition of the word "function" is a potential source of confusion in Sage because there are two types of constructs that are commonly referred to as functions. Mathematicians define a function as a relation that associates each element of a given set (called the domain) with an element of another set (the range). In computer programming, a function is a block of code within a larger program that performs a specific task. Sage supports both types of functions. In order to avoid confusion, we will use the term "callable symbolic expression" to refer to a function in the mathematical sense. The word "function" will refer to a function definition using the Python programming language, which we will learn about in the next section.