A relation is a relationship between sets of values. In math, the relation is between the x-values and y-values of ordered pairs. The set of all x-values is called the domain, and the set of all y-values is called the range.
In this image, we can see that the domain consists of the x-values from each ordered pair. The range consists of the y-values from each ordered pair. The brackets are used to show that the values form a set. It is important to not repeat values in the domain and range sets (notice that two of the ordered pairs have the number 2 as the y-value, but 2 is listed only once in the range). In this example, the values in the domain and range are listed numerically. While this is common practice, it is not essential.
