Cumulative

This is the sum of probabilities
In connection with a normal distribution, a cumulative probability refers to the probability that a ramdonly selected score will be less than (or equal to) a specified value (often referred to as the normal random variable)
Cumulative Distribution Function

Example

Suppose we have a group of 30 people
What is the probability of randomly selecting a person who is 25 years old.
This is an example of simple probability

What is the probability of ramdomly selecting a person who has an age that is less than or equal to 25
This is an example of cumulative probability.