The cumulative distribution function (CDF) calculates the cumulative probability for a given x-value. Use the CDF to determine the probability that a random observation that is taken from the population is less than or equal to a certain value. You can also use this information to determine the probability that an observation is greater than a certain value, or between two values. For example, a cumulative distribution function can show the proportion of trees in a forest that have diameter measurements of 10 inches or less.
If you want to determine the x-value for a specific cumulative probability, use an Inverse Cumulative Distribution Function (ICDF).