Calibrated probability assessment is a way of figuring out how likely something is to happen. To help explain it better, let's use an example. Imagine you have a jar filled with 100 marbles. Some are blue, some are red and some are green. If you want to know how likely it is for you to pick a blue marble, then you can use calibrated probability assessment.
First, you would count how many blue marbles are in the jar. Let's say there are 10 blue marbles. That means out of every 100 marbles, 10 are blue. So out of every 100 tries of picking a marble, you have a 10% or 1 in 10 chance of picking a blue one. That is what calibrated probability assessment is - figuring out how likely something is to happen.