1. The integral of the Probability Density Function (not rigorous)
2. A statistical distribution, indicating the probability of receiving an outcome or a lower ranked outcome for all possible outcomes. The function can range from 0 to 1 (or 100%).

An example of a Cumulative Distribution Function is the well-known "error function" (ERF) whose probability density function is the Normal distribution.
See also: Probability Density Function.