In this chapter we will learn about distributions. Visualizations will be our primary tool for understanding and analyzing distributions.

Terminology. A distribution is a mathematical object that tells us, for each potential value in a dataset, how often that value appears. For example, in a bag with one white ball and one red ball, the distribution of ball colors in the bag can be described as "one white and one red."

A frequency or sometimes probability distribution is a distribution whose amounts have been normalized to add up to 1. That means we divide each count by the total count, producing proportions of the total. The frequency distribution of the ball colors in the bag is "$\frac{1}{2}$ white and $\frac{1}{2}$ red." Notice that the frequency distribution doesn't tell us how many balls are in the bag. Sometimes this is actually a desirable property.

When it's not clear from context whether a distribution describes counts or proportions, we will call non-frequency distributions "count distributions."