The document discusses the normal distribution, which is a specific type of probability distribution where the mean, median, and mode are centered around the middle. It depends on the mean and standard deviation. The document describes the key elements needed to construct a normal distribution like the mean and standard deviation. It also provides an example of calculating the percentage of yearly pizza sales that would be less than $90,000 given the normal distribution of annual sales has a mean of $120,000 and standard deviation of $30,000. Approximately 16% of yearly sales would be less than $90,000.